Topic: 14. Myeloma and other monoclonal gammopathies - Clinical Background: Data from the ongoing phase 2 MagnetisMM-3 (NCT04649359) study demonstrated the efficacy and safety of elranatamab in patients with relapsed/refractory multiple myeloma (RRMM) and no prior BCMA-directed therapy (Cohort A). Aims: To report the efficacy and safety of elranatamab in high-risk subgroups in BCMA-naïve patients from MagnetisMM-3. Methods: Eligibility criteria, dosing and administration were previously reported (Bahlis, ASH 2022). Subgroups analyzed were Revised International Staging System (R-ISS) stage (I/II/III), cytogenetic abnormalities (standard/high risk [high-risk defined by the presence of t(4;14), t(14;16) or del(17p)]), extramedullary disease (EMD) at baseline (Y/N), bone marrow plasma cell involvement (BMPC) at baseline (<50%/≥50%), and penta-refractory disease (Y/N). Results include data up through ~12 months after last patient initial dose. Results: Median treatment durations and the proportions of patients receiving treatment at the data cut-off were lower for all high-risk subgroups than the corresponding lower-risk subgroups (Table). The most frequent cause of discontinuation was progressive disease which was higher for all high-risk subgroups than the corresponding lower risk subgroups. A clinical benefit, assessed by the objective response rate (ORR), was observed across subgroups (Table). A multivariable logistic regression analysis for ORR including baseline age, Eastern Cooperative Oncology Group, sex, region, cytogenetic risk, presence of EMD, BMPC involvement, prior stem cell transplant, R-ISS stage, number of prior lines, type of myeloma, and penta-refractory disease showed presence of EMD at baseline and non-IgG myeloma (vs IgG) as predictive of lower ORR. Light chain-only myeloma (vs IgG) was predictive of higher ORR. Median duration of response (DOR) was not reached in subgroups by 12 months, DOR rate at 12 months is reported in the Table. Any-grade treatment-emergent adverse events (TEAEs) were reported in 100% of patients in the study. The incidence of grade 3/4 TEAEs was overall similar across subgroups (Table). Summary/Conclusion: Elranatamab is efficacious and has a manageable safety profile in patients with high-risk RRMM and no prior BCMA-directed therapy. Table - R-ISS stage I R-ISS stage II R-ISS stage III Standard cytogenetic risk High cytogenetic risk (n=28) (n=68) (n=19) (n=83) (n=31) Median treatment duration (mo) 10.7 5.7 1.4 7.9 2.6 Receiving treatment at data cut-off (%) 42.9 38.2 5.3 41.0 19.4 ORR (%, 95% CI) 75.0 63.2 26.3 63.9 54.8 (55.1, 89.3) (50.7, 74.6) (9.1, 51.2) (52.6, 74.1) (36.0, 72.7) DOR rate at 12 mo (%, 95% CI) 76.2 78.8 53.3 79.4 57.0 (45.4, 91.0) (61.8, 88.8) (6.8, 86.3) (63.4, 89.0) (27.4, 78.3) Grade 3/4 TEAEs (%) 75.0 73.5 63.2 73.5 64.5 - EMD – N EMD – Y <50% BMPC ≥50% BMPC Penta-refractory disease – N Penta-refractory disease - Y (n=84) (n=39) (n=89) (n=26) (n=71) (n=52) Median treatment duration (mo) 8.4 2.2 8.2 3.0 10.0 2.3 Receiving treatment at data cut-off (%) 38.1 25.6 38.2 26.9 42.3 23.1 ORR (%, 95% CI) 71.4 38.5 67.4 46.2 71.8 46.2 (60.5, 80.8) (23.4, 55.4) (56.7, 77.0) (26.6, 66.6) (59.9, 81.9) (32.2, 60.5) DOR rate at 12 mo (%, 95% CI) 73.8 73.4 72.0 81.5 74.7 71.9 (58.3, 84.3) (37.4, 90.8) (56.6, 82.7) (43.5, 95.1) (58.6, 85.3) (41.2, 88.4) Grade 3/4 TEAEs (%) 77.4 56.4 73.0 69.2 73.2 67.3 Keywords: Myeloma, Bispecific, Multiple myeloma, Clinical trial

8008 Background: Studies in the MagnetisMM program (MM-1, NCT03269136; MM-3, NCT04649359; MM-9, NCT05014412) enrolled pts treated with prior BCMA-directed therapies. A pooled analysis from these studies evaluated the efficacy and safety of elranatamab in pts with RRMM and prior exposure to BCMA-directed therapy. Methods: Eligible pts received at least 1 PI, 1 IMiD, 1 anti-CD38 antibody, and 1 BCMA-directed therapy (ADC and/or CAR-T cells). Pooled analysis included pts in MM-1 (n = 13) who received SC elranatamab 215−1000 µg/kg; MM-3 (n = 64) and MM-9 (n = 9) who received the RP2D, SC 76 mg QW. Efficacy endpoints were assessed by investigator per IMWG criteria. TEAEs were graded by CTCAE (MM-1, v4.03; MM-3 & MM-9, v5.0); CRS and ICANS were graded by ASTCT criteria. Results include data up through ~10 months after last pt initial dose in all pooled studies. Results: In total, 86 pts were included. Median age was 66.0 y (range, 40−84); 47.7% male. At baseline, 69.8% had an ECOG PS ≥1; 24.4% had high risk cytogenetics; 54.7% had extramedullary disease. Pts received a median of 7.0 (3−19) prior lines of therapy, including BCMA-directed ADC (67.4%), CAR T-cells (41.9%), 9.3% received both. 96.5% and 54.7% of pts were triple-class and penta-drug refractory, respectively; among pts who received ADC and CAR-T cells respectively, 79.3% and 27.8% were refractory to ADC and CAR-T cells. After a median follow-up of 10.3 mo (0.3−32.3), median duration of treatment was 3.3 mo (0.03−30.4). At data cut-off, 24.4% of pts remained on treatment; most common reason for permanent treatment discontinuation was progressive disease (44.2%). ORR was 45.3% (95% CI 34.6−56.5), with ≥CR achieved in 17.4% of pts. ORR for pts with prior BCMA-directed ADC and CAR-T cells was 41.4% (95% CI 28.6−55.1) and 52.8% (95% CI 35.5−69.6), respectively. Among responders, median time to objective response was 1.9 mo (0.3−9.3). Median DOR was not reached by 10 mo; the DOR rate at 9 mo was 72.4% (95% CI 54.7−84.2). DOR rate (95% CI) for pts with prior BCMA-directed ADC and CAR-T cells were 67.3% (43.1−83.0) and 78.9% (53.2−91.5) at 9 mo, respectively. Median PFS was 4.8 mo (95% CI 1.9−7.7), and median OS was not reached by 10 mo, with a rate of 60.1% (95% CI 48.9−69.6) at 9 mo. Most common (≥25% of pts) TEAEs were CRS (65.1% [G3 1.2%]), anemia (59.3% [G3/4, 46.5%]), neutropenia (44.2% [G3/4, 40.7%]), thrombocytopenia (40.7% [G3/4, 29.1%]), diarrhea (33.7% [G3/4, 0%], and lymphopenia (32.6% [G3/4, 30.2%]). ICANS was reported in 5.8% (G3, 2.3%) of pts. Conclusions: In pts with RRMM and prior exposure to BCMA-directed therapies, elranatamab was efficacious and well tolerated; no new safety signals were observed vs the BCMA-naïve population. Results support treatment with elranatamab in pts with RRMM post BCMA-directed therapy. Clinical trial information: NCT03269136 , NCT04649359 , NCT05014412 .

BACKGROUND In the phase 2, registrational MagnetisMM-3 (NCT04649359) trial, patients with RRMM who had not previously received a B cell maturation antigen (BCMA)-directed therapy (n=123) achieved an objective response rate of 61% with single-agent elranatamab (ELRA), a BCMA-CD3 bispecific antibody. Common treatment-emergent adverse events (TEAEs) included infections (70%; 40% grade [G] 3/4) and CRS (58%; all G1/2). Here we report on the safety of ELRA in the MagnetisMM-17 (MM-17; NCT05462639) trial, a North American Expanded Access Protocol (EAP). METHODS MM-17 is an ongoing, single-arm, open-label study for patients with triple-class refractory RRMM (refractory to ≥1 proteasome inhibitor, ≥1 immunomodulatory drug, and ≥1 anti-CD38 antibody), and who had no prior BCMA-directed therapy. Patients must be ≥18 years of age and have a confirmed diagnosis of MM, measurable disease by IMWG criteria, an Eastern Cooperative Oncology Group performance status (ECOG PS) of 0-1, adequate organ function, and no active, uncontrolled infection. The study is being conducted in the US and Canada. The primary objective is to provide access to ELRA for patients with RRMM and no access to comparable/alternative therapy. The secondary objective is to evaluate the safety and tolerability of ELRA. Patients received subcutaneous ELRA 76 mg once every week on a 28-day cycle after step-up doses of 12 and 32 mg during week 1. Dose frequency was reduced to once every 2 weeks (Q2W) after ≥6 cycles in patients with persistent response (≥partial response), and then from Q2W to Q4W after ≥6 Q2W cycles. Patients received ELRA until disease progression, unacceptable toxicity, withdrawal of consent, study termination, or ELRA becomes commercially available. TEAEs were graded by NCI CTCAE v5.0, except cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) which were graded according to the American Society for Transplantation and Cellular Therapy criteria (ASTCT). RESULTS As of April 28, 2023, 20 patients had enrolled in the trial. Median patient age was 72.5 years (range 53-82); 50% male, 85% white, and 15% Black/African American. At baseline, most patients had an ECOG PS of 1 (95%), and 40% had R-ISS disease stage III. Patients had a median of 4 prior lines of therapy (range 2-8); 95% and 35% of patients had triple-class and penta-drug refractory disease, respectively. At the time of data cut-off, 2 patients had discontinued due to progressive disease. Median treatment duration was 0.95 months (range 0.26-2.83); median relative dose intensity was 98.3% (range 48-105). TEAEs were reported in all 20 patients, with G3 or G4 events reported in 13 (65%). There were no G5 events. Thirteen (65%) patients developed CRS, all events were G1 (50%) or G2 (15%); no events G ≥3 were reported. After the first step-up dose, 11 (55%) patients had a CRS event. CRS events occurred in 3 patients (15%) and 1 patient (5%) after the second step-up dose and first treatment dose, respectively. The median time to onset was 2 days (range 1-4), and the median time to resolution was 3 days (range 1-5). ICANS occurred in 2 of the 20 patients (10%), both events were G1, with 1 occurring after the first step-up dose and the other after the second step-up dose. The median time to onset was 3 days (range 3-3) and the median time to resolution was 2.5 days (range 2-3). Four (20%) patients had infections, including 1 event each of G1 sinusitis, G2 acute sinusitis, G2 folliculitis, G2 upper respiratory tract infection and G3 bacterial conjunctivitis. Cytopenias were reported in 11 (55%) patients. The most common (occurring in ≥3 [15%] patients) cytopenias were neutropenia (30%; G3/4 25%), lymphopenia (20%; G3/4 15%), and thrombocytopenia (15%; G3/4 10%). CONCLUSIONS Early safety data (median treatment duration <1 month) from this ongoing expanded access protocol of elranatamab in patients with RRMM are consistent with results from the phase 2, registrational MagnetisMM-3 trial, with no new safety signal identified.

8048 Background: Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that leverages aminopeptidases and rapidly releases alkylating agents inside tumor cells. Melflufen has a mechanism of action distinct from other alkylating agents (Slipicevic et al. AACR 2020. Abs. 1843). In the O-12-M1 (NCT01897714) and HORIZON (OP-106; NCT02963493) studies, melflufen plus dex showed meaningful efficacy and a clinically manageable safety profile in pts with RRMM (Richardson et al. Lancet Haematol. 2020;7:5; Richardson et al. J Clin Oncol. 2020;Dec 9 [Epub]). This pooled analysis examines pts from these studies exposed to prior alkylators. Methods: Both the O-12-M1 and HORIZON studies included pts with RRMM who received ≥ 2 prior lines of therapy (LoTs) and had a primary endpoint of overall response rate (ORR). Secondary endpoints included progression-free survival (PFS) and safety. Data from the 2 studies were pooled and analyzed according to previous exposure and refractoriness to alkylators before study entry. Refractoriness to prior alkylator therapy was defined as disease that failed to achieve a minimal response or progressed while on therapy, or within 60 d of last therapy. Results: Of 202 pts (HORIZON: n = 157, cutoff January 14, 2020; O-12-M1: n = 45, cutoff October 29, 2019), 178 (88%) had been exposed to alkylators in ≥ 1 prior LoT (see Table for subgroups). Pts exposed and refractory to alkylators in ≥ 2 LoTs had the highest number of pts refractory to an alkylator in the last LoT (61%), and 82% were refractory to an alkylator within 12 mo of study entry. Meaningful response rates were seen in all subgroups, except for pts who were exposed and refractory to alkylators in ≥ 2 prior LoTs (see Table). PFS trended toward being shorter with higher exposure and refractoriness to prior alkylators. Results should be interpreted with caution due to limited pt numbers. Grade 3/4 adverse events (AEs) were similar between pts exposed to prior alkylators (O-12-M1: 85%; HORIZON: 89%) and the overall population (O-12-M1: 84%; HORIZON: 89%). The most common AEs were hematologic, but were mostly reversible and clinically manageable. Nonhematologic AEs were infrequent and primarily grade 1/2. Conclusions: Melflufen in combination with dex showed meaningful efficacy and a clinically manageable safety profile in pts with RRMM exposed/refractory to prior alkylators. Clinical trial information: NCT02963493 and NCT01897714. [Table: see text]

Relapsed/refractory multiple myeloma (RRMM) is known to have a high burden of disease and complications associated with refractoriness to prior lines of therapy. Severe pain and fatigue symptoms and impairments in physical and emotional functioning have been strongly linked to reduced health-related quality of life (HRQoL) in patients with RRMM. Assessment of patient reported-outcome measures from the pivotal, Phase II HORIZON study (OP-106; NCT02963493) in patients with RRMM (n = 64) demonstrated that melphalan flufenamide (melflufen) plus dexamethasone treatment preserved HRQoL. Patients had clinically meaningful improvements, even after eight treatment cycles, in relevant scales such as global health status/QoL, physical functioning, emotional functioning, pain, and fatigue. Patients with triple-class-refractory disease (n = 50) displayed similar improvements. Patient-reported outcome deterioration was delayed for a substantial amount of time in patients who experienced a response to melflufen plus dexamethasone treatment relative to patients who did not experience a response. These findings support the notion that treatment with melflufen plus dexamethasone may sustain or improve HRQoL over time in patients with RRMM, including in patients with triple-class-refractory disease for whom outcomes are generally worse. The clinical benefits observed in patients from the HORIZON trial are encouraging and supportive of translation into real-world practice.

Background: EMD is characterized by a subclone of aggressive MM cells that thrive and grow independent of the bone marrow microenvironment and is often associated with poor-risk features including high-risk cytogenetics, increased proliferation, evasion of apoptosis, and resistance to therapies in MM (Bladé et al. J Clin Oncol. 2011;29:3805; Deng et al. Clin Lymphoma Myeloma Leuk. 2015;15:286). Prognosis for pts with EMD is poor, particularly in the RRMM setting. Additionally, prognosis is usually poorer for pts with hematogenous-spread soft-tissue plasmacytomas than for those with bone-related plasmacytomas (Gagelmann et al. Haematologica. 2018;103:890; Mangiacavalli et al. Ann Hematol. 2017;96:73). No standard therapy has been established for this high-unmet need population (Usmani et al. Blood. 2016;128:37; Jimenez-Segura et al. Eur J Haematol. 2019;102:389), and outcomes are considerably worse than those for pts without EMD; for example, a recent analysis of isatuximab + pomalidomide + dex showed a median progression free survival (PFS) of 4.6 mo vs 11.5 mo in the total population (Beksac et al. EHA 2020. Abs. EP978). Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. In the phase 2 HORIZON study (OP-106; NCT02963493), melflufen + dex showed clinically meaningful efficacy (overall response rate [ORR], 29%; median PFS, 4.2 mo; median overall survival [OS], 11.6 mo) and a manageable safety profile in pts with heavily pretreated RRMM, including in pts with triple-class-refractory MM (Richardson et al. EHA 2020. Abs. EP945). This analysis presents additional data for the largest cohort of pts with EMD in a clinical trial setting to date. Methods: Pts with RRMM must have received ≥2 lines of prior therapy, including an IMiD and a proteasome inhibitor, and been refractory to pomalidomide and/or an anti-CD38 monoclonal antibody. Pts received melflufen 40 mg (intravenous; d1 of each 28-d cycle) and dex 40 mg/wk until progressive disease or unacceptable toxicity. The primary endpoint was ORR (≥ partial response [PR]; investigator-assessed per International Myeloma Working Group [IMWG] criteria). Secondary endpoints included PFS, OS, duration of response (DOR), and safety. For pts with known or suspected EMD, defined as either isolated soft-tissue and/or bone-related extramedullary plasmacytomas with soft-tissue extension, an assessment was required at screening and to confirm a response per IMWG criteria. Results: Of 157 pts enrolled and treated (data cutoff date, Jan 14, 2020), 55 (35%) had EMD (49% soft-tissue and 51% bone-related soft-tissue plasmacytoma). In pts with EMD, median age was 64 y (range, 43-82); median time since diagnosis was 5.6 y (range, 0.7-14.5); 35% had high-risk cytogenetics; 33% had International Staging System stage 3; median prior lines of therapy was 5 (range, 2-12); 60% had disease that was refractory to prior alkylator therapy; and 91% had triple-class-refractory MM. ORR (95% CI) was 24% (13-37) in pts with EMD and 29% (22-37) overall (N=157). In pts with EMD and the overall population, respectively, median (95% CI) DOR was 5.5 mo (1.8-not evaluable [NE]) and 5.5 mo (3.9-7.6), PFS was 2.9 mo (2.0-3.8) and 4.2 mo (3.4-4.9), and median OS was 6.5 mo (5.1-9.7) and 11.6 mo (9.3-15.4;) (Table). In pts with EMD who achieved ≥PR (n=13), median (95% CI) PFS was 17.3 mo (5.3-NE), and OS was 18.5 mo (8.7-NE). Due to low event numbers, the results in pts with ≥PR may be overestimated. The safety profile of melflufen + dex in pts with EMD was consistent with that in the overall population, with grade 3/4 treatment-emergent adverse events (TEAEs) reported in 78% and 89% of pts, respectively. In pts with EMD, the most common grade 3/4 TEAEs were anemia (42%), thrombocytopenia (40%), and neutropenia (38%); the most common nonhematologic grade 3/4 TEAE of interest was pneumonia (9%). No treatment-related deaths with melflufen + dex were reported. Conclusions: Melflufen + dex showed activity in advanced RRMM with EMD, with encouraging PFS and OS in pts with confirmed stable disease or better. The safety profile of melflufen + dex was consistent with previous reports. To date, this clinical study provides the largest cohort of pts with EMD demonstrating benefit in this population with a high unmet medical need. These data support further evaluation of melflufen + dex in RRMM with EMD. Disclosures Richardson: Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. Mateos:AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees. Oriol:Janssen: Consultancy; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Larocca:Amgen: Honoraria; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees. Cavo:AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; GlaxoSmithKline: Honoraria, Speakers Bureau; Karyopharm: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Rodríguez-Otero:Abbvie: Consultancy; Oncopeptides: Consultancy; Medscape: Membership on an entity's Board of Directors or advisory committees; Celgene/Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Amgen: Honoraria; GlaxoSmithKline: Consultancy, Current Employment, Current equity holder in publicly-traded company; Kite: Consultancy; Sanofi: Consultancy. Leleu:AbbVie: Honoraria; Carsgen: Honoraria; Incyte: Honoraria; Merck: Honoraria; Oncopeptide: Honoraria; Karyopharm: Honoraria; Sanofi: Honoraria; GSK: Honoraria; Amgen: Honoraria; Novartis: Honoraria; BMS-celgene: Honoraria; Janssen: Honoraria. Nadeem:Amgen: Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Adaptive: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Hassoun:Takeda: Research Funding; Celgene: Research Funding; Novartis: Consultancy. Touzeau:Abbvie: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding; Sanofi: Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Amgen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; GlaxoSmithKline: Honoraria, Research Funding. Amor:GSK: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene-BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees. Maisel:Texas Oncology: Current Employment; Amgen: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Kite: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau. Mazumder:Amgen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; The Oncology Institute: Current Employment. Raptis:UPMC: Current Employment; INTEGRA: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Puig:THE BINDING SITE: Consultancy, Honoraria; TAKEDA: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; JANSSEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; BRISTOL-MYERS SQUIBB: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; CELGENE: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; AMGEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding. Zamagni:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Speakers Bureau; Takeda: Honoraria, Other: Travel, Accommodations, Expenses, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Speakers Bureau; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Speakers Bureau; Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Thuresson:Oncopeptides: Consultancy, Current equity holder in publicly-traded company; Statisticon: Current Employment. Harmenberg:Ultupharma AB: Current equity holder in private company; Medivir AB: Current equity holder in publicly-traded company; Oncopeptides AB: Consultancy, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Harlin:Oncopeptides AB: Consultancy, Current equity holder in publicly-traded company. Blade Creixenti:Takeda: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees. OffLabel Disclosure: This is a phase 2 investigational study of melflufen in RRMM.

Background: In patients with relapsed/refractory multiple myeloma (RRMM), 29%-59% have high-risk (HR) cytogenetic abnormalities that are associated with poor treatment outcomes (Kumar et al. Leukemia. 2017;31:2443; Gandhi et al. Leukemia. 2019;33:2266). Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. Melflufen plus dexamethasone (dex) showed clinically meaningful efficacy and a manageable safety profile in patients with heavily pretreated and poor-risk RRMM in the phase 2 HORIZON study (OP-106; NCT02963493; Richardson et al. EHA 2020. Abs. EP945). The overall response rate (ORR) was 29%, median progression-free survival (PFS) was 4.2 months, and median overall survival (OS) was 11.6 months. The most common nonhematologic grade 3/4 adverse event (AE) was pneumonia (10%). This is an analysis of the cytogenetic profile and a comparison of the efficacy for patients with and without HR cytogenetic abnormalities in the HORIZON study. Methods: Patients with RRMM had received ≥2 lines of prior therapy, including an IMiD and a proteasome inhibitor, and were refractory to pomalidomide and/or an anti-CD38 monoclonal antibody. Patients received melflufen 40 mg (intravenously on day 1 of each 28-day cycle) and dex 40 mg/wk until progressive disease or unacceptable toxicity. The primary endpoint was ORR (≥ partial response [PR]; investigator-assessed per International Myeloma Working Group criteria); secondary endpoints included PFS, OS, duration of response (DOR), and safety. At screening, cytogenetics were evaluated using plasma cells from bone marrow aspirate by interphase fluorescence in situ hybridization and by conventional karyotyping. HR cytogenetic abnormalities were classified by the presence of t(4;14), t(14;16), t(14;20), del(17/17p), or gain(1q) (Sonneveld et al. Blood. 2016;127:2955). Results: Of the 157 patients enrolled and treated (data cutoff date, January 14, 2020), 59 (38%) had HR cytogenetic abnormalities at screening. Cytogenetic status was missing/unknown in 31 patients (20%). Among patients with HR cytogenetics, gain(1q) was seen in 41 (69%), del(17p) in 31%, t(4:14) in 31%, t(14:16) in 7%, and t(14:20) in none. Although baseline characteristics were generally similar between patients with and without HR cytogenetics (Table), fewer patients with HR cytogenetics had triple-class-refractory MM (69%) than those without HR cytogenetics (80%). The ORR (95% CI) was 20% (11-33) in patients with HR cytogenetics and 35% (25-45) in patients without HR cytogenetics. Among responding patients with HR cytogenetics (n=12), 4 achieved a very good PR and 8 a PR, with a median DOR of 6.7 months (95% CI, 3.0-not evaluable). Median DOR was 5.1 months (95% CI, 3.9-7.5) in patients without HR cytogenetics (n=34). Median PFS was 3.1 months (95% CI, 2.1-5.4) and 4.4 months (95% CI, 3.8-5.1), respectively, and OS was 11.5 months (95% CI, 8.5-13.6) and 13.2 months (95% CI, 8.1-17.6), respectively, in patients with and without HR cytogenetics. Among patients with HR cytogenetics, the ORR was 24% (95% CI, 11-40) in patients with 1 HR cytogenetic abnormality (n=38) and 14% (95% CI, 3-36) in patients with ≥2 HR cytogenetic abnormalities (n=21). Median PFS was 2.9 months (95% CI, 1.9-7.6) and 4.4 months (95% CI, 1.9-6.5), and OS was 11.6 months (95% CI, 7.7-21.1) and 11.5 months (95% CI, 4.5-13.9) in patients with 1 and ≥2 HR cytogenetic abnormalities, respectively. In patients with HR cytogenetics (n=59) and the overall population (N=157), grade 3/4 AEs were reported in 92% and 89%, respectively; the most common grade 3/4 AEs were thrombocytopenia (51% and 57%), neutropenia (47% and 53%), and anemia (36% and 43%); the most common nonhematologic grade 3/4 AE was pneumonia (17% and 10%). Serious AEs occurred in 54% of patients with HR cytogenetics and in 49% of patients in the overall population, most commonly pneumonia (17% and 9%, respectively). Conclusions: In the HORIZON study, melflufen plus dex also showed efficacy in patients with HR cytogenetics. The safety profile of melflufen plus dex in patients with HR cytogenetics was consistent with that of the overall population. Taken together, these data support further evaluation of melflufen plus dex in RRMM with HR cytogenetics. Disclosures Mateos: GlaxoSmithKline: Honoraria; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Oriol:Janssen: Consultancy; Amgen: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees. Larocca:Amgen: Honoraria; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees. Blade Creixenti:Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Cavo:BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; GlaxoSmithKline: Honoraria, Speakers Bureau; Karyopharm: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Rodríguez-Otero:Kite: Consultancy; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Sanofi: Consultancy; Abbvie: Consultancy; Medscape: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Celgene/Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); GlaxoSmithKline: Consultancy, Current Employment, Current equity holder in publicly-traded company; Oncopeptides: Consultancy. Leleu:BMS-celgene: Honoraria; Janssen: Honoraria; Sanofi: Honoraria; GSK: Honoraria; AbbVie: Honoraria; Oncopeptide: Honoraria; Karyopharm: Honoraria; Amgen: Honoraria; Carsgen: Honoraria; Incyte: Honoraria; Merck: Honoraria; Novartis: Honoraria. Nadeem:Adaptive: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Amgen: Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Hassoun:Takeda: Research Funding; Celgene: Research Funding; Novartis: Consultancy. Touzeau:Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Sanofi: Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Takeda: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding. Amor:Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene-BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees. Maisel:Texas Oncology: Current Employment; Texas Oncology: Current Employment; Amgen: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau. Mazumder:Takeda: Honoraria, Speakers Bureau; The Oncology Institute: Current Employment; Celgene: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau. Raptis:INTEGRA: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; UPMC: Current Employment. Puig:CELGENE: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; AMGEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; JANSSEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; THE BINDING SITE: Consultancy, Honoraria; TAKEDA: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; BRISTOL-MYERS SQUIBB: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau. Harmenberg:Oncopeptides AB: Consultancy, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Medivir AB: Current equity holder in publicly-traded company; Ultupharma AB: Current equity holder in private company. Gustavsson:Vinnova: Honoraria; XSpray AB: Divested equity in a private or publicly-traded company in the past 24 months; Celgene: Divested equity in a private or publicly-traded company in the past 24 months; Bristol-Myers Squibb: Divested equity in a private or publicly-traded company in the past 24 months; Sangus Jazz AB: Current equity holder in private company; PiezoMotor AB: Current equity holder in publicly-traded company; Episurf AB: Current equity holder in publicly-traded company; Nanexa AB: Current equity holder in publicly-traded company, Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides AB: Current Employment, Current equity holder in publicly-traded company. Thuresson:Oncopeptides: Consultancy, Current equity holder in publicly-traded company; Statisticon: Current Employment. Richardson:Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. OffLabel Disclosure: This is a phase 2 investigational study of melflufe in RRMM.

PURPOSE Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate that targets aminopeptidases and rapidly and selectively releases alkylating agents into tumor cells. The phase II HORIZON trial evaluated the efficacy of melflufen plus dexamethasone in relapsed and refractory multiple myeloma (RRMM), a population with an important unmet medical need. PATIENTS AND METHODS Patients with RRMM refractory to pomalidomide and/or an anti-CD38 monoclonal antibody received melflufen 40 mg intravenously on day 1 of each 28-day cycle plus once weekly oral dexamethasone at a dose of 40 mg (20 mg in patients older than 75 years). The primary end point was overall response rate (partial response or better) assessed by the investigator and confirmed by independent review. Secondary end points included duration of response, progression-free survival, overall survival, and safety. The primary analysis is complete with long-term follow-up ongoing. RESULTS Of 157 patients (median age 65 years; median five prior lines of therapy) enrolled and treated, 119 patients (76%) had triple-class–refractory disease, 55 (35%) had extramedullary disease, and 92 (59%) were refractory to previous alkylator therapy. The overall response rate was 29% in the all-treated population, with 26% in the triple-class–refractory population. In the all-treated population, median duration of response was 5.5 months, median progression-free survival was 4.2 months, and median overall survival was 11.6 months at a median follow-up of 14 months. Grade ≥ 3 treatment-emergent adverse events occurred in 96% of patients, most commonly neutropenia (79%), thrombocytopenia (76%), and anemia (43%). Pneumonia (10%) was the most common grade 3/4 nonhematologic event. Thrombocytopenia and bleeding (both grade 3/4 but fully reversible) occurred concomitantly in four patients. GI events, reported in 97 patients (62%), were predominantly grade 1/2 (93%); none were grade 4. CONCLUSION Melflufen plus dexamethasone showed clinically meaningful efficacy and a manageable safety profile in patients with heavily pretreated RRMM, including those with triple-class–refractory and extramedullary disease.

Background: Pts with RRMM are a very sick population due to disease symptoms, comorbidities, side effects from treatments, and age-related fragility (Chim et al. Leukemia. 2018;32:252). Pts often experience adverse events (AEs) that affect their quality of life and reduce treatment compliance; hematologic AEs are frequent. Inpatient services for the management of AEs are often necessary and a major cost driver, with costs rising per AE episode (highest for hematologic AEs; Felber et al. ASH 2019. Abs. 4725). Additionally, a real-world study suggested that >50% of pts with hematologic AEs require readmittance to the hospital after initial treatment (Yeaw et al. ISPOR 2020. Abs. PCN78). Published data to date come from real-world evidence, with limited reports from clinical trials. Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. In the pivotal, phase 2, HORIZON study (OP-106; NCT02963493), melflufen plus dex showed clinically meaningful efficacy and a safety profile consisting primarily of clinically manageable hematologic AEs in pts with heavily pretreated RRMM (Richardson et al. EHA 2020. Abs EP945). This analysis aids to further elucidate the healthcare resource utilization of pts with RRMM treated with melfulfen in a clinical trial by evaluating the impact of AEs on hospitalizations in HORIZON. Methods: Pts with RRMM who had received ≥2 lines of prior therapy, including an IMiD and a proteasome inhibitor and were refractory to pomalidomide and/or an anti-CD38 monoclonal antibody were treated with melflufen and dex as described (Richardson et al. EHA 2020. Abs EP945). Data for specific AEs potentially related to the study drugs (melflufen and/or dex; TRAEs) requiring hospitalizations >24 h were compared with all potential TRAEs and within each preferred term with >1 event reported regardless of hospitalization. AEs were classified as TRAE if reported as related or possibly related to either study drug by the treating physician. Results: At the data cutoff date (14 Jan 2020), 157 pts were enrolled and had received ≥1 dose of study treatment; 35 (22%) had been hospitalized due to a TRAE. Pts hospitalized due to TRAEs had a median age of 63 y (range, 43-84); 31% had International Staging System stage 3 disease; 49% had high-risk cytogenetics; and 77% had triple-class-refractory MM. In the overall population (N=157), the most frequent grade 3/4 treatment-emergent AEs (TEAEs) were thrombocytopenia (57%), neutropenia (53%), and anemia (43%). Serious AEs occurred in 49% of pts, most commonly pneumonia (9%) and febrile neutropenia (5%). Of all 3713 TEAEs, 118 (3.2%) led to hospitalization. Of 2688 TRAEs, 58 (2.2%) resulted in hospitalization. Pneumonia and febrile neutropenia TRAEs resulted in the most hospitalizations, with 11 events (78.6% of pneumonia TRAEs; 0.41% of all TRAEs) and 10 events (83.3% of febrile neutropenia TRAEs; 0.37% of all TRAEs), respectively (Table). Grade 3/4 hematologic TRAEs resulting in hospitalization included thrombocytopenia (9 hospitalizations; 1.4% of thrombocytopenia TRAEs; 0.33% of all TRAEs) and neutropenia (2 hospitalizations; 0.3% of neutropenia TRAEs; 0.07% of all TRAEs). All TRAEs that resulted in hospitalization were grade 3/4 except for 2 events (1 pyrexia [grade 1]; 1 pneumonia [grade 2]). For 3 of 9 thrombocytopenia events and 1 of 2 neutropenia events, it was unclear whether the hospitalization was >24 h; however, they were included in current analysis. Conclusion: Within this heavily pretreated pt population, most TRAEs could be managed without the need for hospitalization. Hematologic AEs were common but led to few hospitalizations overall. Although 11 cases (78.6%) of TRAEs of pneumonia required hospitalization, these events represent only 0.41% of all TRAEs, and infections are normally expected in advanced RRMM (Blimark et al. Plasma Cell Disorders. 2015;100:107). Use of inpatient services are a major driver of economic burden in RRMM and have been shown to be highly utilized in less heavily pretreated populations than HORIZON (Yeaw et al. ISPOR 2020. Abs. PCN7; Felber et al. ASH 2019. Abs. 4725). Results of this analysis suggest limited use of inpatient services for TRAEs with melflufen plus dex. Further analyses of real-world data on melflufen are warranted to confirm the results presented from this analysis. Disclosures Nadeem: Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Adaptive: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Richardson:Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. Mateos:Adaptive: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees. Oriol:GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy. Larocca:GSK: Honoraria; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees. Blade Creixenti:Amgen: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees. Rodríguez-Otero:Celgene/Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); GlaxoSmithKline: Consultancy, Current Employment, Current equity holder in publicly-traded company; Oncopeptides: Consultancy; Abbvie: Consultancy; Kite: Consultancy; Medscape: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Sanofi: Consultancy; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Leleu:Oncopeptide: Honoraria; Karyopharm: Honoraria; Sanofi: Honoraria; GSK: Honoraria; Amgen: Honoraria; Novartis: Honoraria; BMS-celgene: Honoraria; AbbVie: Honoraria; Carsgen: Honoraria; Incyte: Honoraria; Merck: Honoraria; Janssen: Honoraria. Hassoun:Novartis: Consultancy; Takeda: Research Funding; Celgene: Research Funding. Touzeau:Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Sanofi: Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Abbvie: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding; GlaxoSmithKline: Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses. Amor:GSK: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene-BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Maisel:Texas Oncology: Current Employment; Amgen: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Celgene: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau. Mazumder:Celgene: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; The Oncology Institute: Current Employment. Raptis:UPMC: Current Employment; INTEGRA: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Puig:BRISTOL-MYERS SQUIBB: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; CELGENE: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; AMGEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; THE BINDING SITE: Consultancy, Honoraria; JANSSEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; TAKEDA: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding. Sandberg:Oncopeptides AB: Current Employment; Novo Nordisk AS: Divested equity in a private or publicly-traded company in the past 24 months, Ended employment in the past 24 months. Pelaez:Märsta Läkarhus AB: Ended employment in the past 24 months; Oncopeptides: Consultancy. Jaques:Pharma Biotech Consultants: Consultancy; Oncopeptides: Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Pfizer: Consultancy; Morphosys AG: Consultancy; Oncopeptides: Ended employment in the past 24 months. Orre:Oncopeptides: Current Employment. Cavo:GlaxoSmithKline: Honoraria, Speakers Bureau; Karyopharm: Honoraria; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. OffLabel Disclosure: This is phase 2 investigational study of melflufen in RRMM.

Context: Outcomes in RRMM remain poor (Kumar et al. Leukemia. 2017; 31:2443), and treatment options are limited for RRMM refractory to multiple drug classes (Gandhi et al. Leukemia. 2019; 33:2266). Melphalan flufenamide (melflufen) is a first-in-class anticancer peptide-drug conjugate that rapidly delivers an alkylating payload into tumor cells. A phase 1/2 study established the dosage of melflufen plus dexamethasone in RRMM (Richardson et al. Lancet Haematol. 2020; 7:e395). Objective: Evaluate the efficacy and safety of melflufen plus dexamethasone in RRMM in the pivotal, single-arm, multicenter, phase 2 HORIZON study (NCT02963493). Methods: Patients who had RRMM, ≥2 prior lines of therapy (≥1 IMiD + ≥1 proteasome inhibitor [PI]), and were refractory to pomalidomide and/or an anti-CD38 mAb received melflufen plus dexamethasone until progressive disease or unacceptable toxicity. Primary endpoint: overall response rate (ORR; investigator-assessed per IMWG criteria). Secondary endpoints: duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Subgroup analyses: triple-class–refractory (TCR) disease (refractory to or intolerant of ≥1 IMiD + ≥1 PI + ≥1 anti-CD38 mAb) and extramedullary disease (EMD). Results: Of 157 patients treated (intention-to-treat [ITT]); 26 remain on study (data cutoff: January 14, 2020). Median age: 65 years (range, 35-86); 25% had ISS stage III disease; and 35% had EMD. Median prior lines of therapy: 5 (range, 2-12); 76% had TCR disease. In the ITT, ORR was 29% (95% CI, 22-37); median (95% CI) DOR was 5.5 months (3.9-7.6); PFS was 4.2 months (3.4-4.9); and OS was 11.6 months (9.3-15.4). In patients with TCR disease and EMD, ORR was 26% (95% CI, 18-35) and 24% (95% CI, 13-37), respectively; DOR, PFS, and OS will be presented. Most common grade 3/4 adverse events (AEs): neutropenia (79%), thrombocytopenia (76%), and anemia (43%). Most common nonhematologic grade 3/4 AEs: pneumonia (10%) and hypophosphatemia (5%). AEs led to melflufen dose reduction and discontinuation in 27% and 22% of patients, respectively. Most common serious AEs were pneumonia (9%) and febrile neutropenia (5%). No treatment-related deaths. Conclusion: Melflufen plus dexamethasone showed clinically meaningful efficacy with a manageable safety profile in heavily pretreated RRMM, including in patients with TCR disease and EMD. Outcomes in RRMM remain poor (Kumar et al. Leukemia. 2017; 31:2443), and treatment options are limited for RRMM refractory to multiple drug classes (Gandhi et al. Leukemia. 2019; 33:2266). Melphalan flufenamide (melflufen) is a first-in-class anticancer peptide-drug conjugate that rapidly delivers an alkylating payload into tumor cells. A phase 1/2 study established the dosage of melflufen plus dexamethasone in RRMM (Richardson et al. Lancet Haematol. 2020; 7:e395). Evaluate the efficacy and safety of melflufen plus dexamethasone in RRMM in the pivotal, single-arm, multicenter, phase 2 HORIZON study (NCT02963493). Patients who had RRMM, ≥2 prior lines of therapy (≥1 IMiD + ≥1 proteasome inhibitor [PI]), and were refractory to pomalidomide and/or an anti-CD38 mAb received melflufen plus dexamethasone until progressive disease or unacceptable toxicity. Primary endpoint: overall response rate (ORR; investigator-assessed per IMWG criteria). Secondary endpoints: duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Subgroup analyses: triple-class–refractory (TCR) disease (refractory to or intolerant of ≥1 IMiD + ≥1 PI + ≥1 anti-CD38 mAb) and extramedullary disease (EMD). Of 157 patients treated (intention-to-treat [ITT]); 26 remain on study (data cutoff: January 14, 2020). Median age: 65 years (range, 35-86); 25% had ISS stage III disease; and 35% had EMD. Median prior lines of therapy: 5 (range, 2-12); 76% had TCR disease. In the ITT, ORR was 29% (95% CI, 22-37); median (95% CI) DOR was 5.5 months (3.9-7.6); PFS was 4.2 months (3.4-4.9); and OS was 11.6 months (9.3-15.4). In patients with TCR disease and EMD, ORR was 26% (95% CI, 18-35) and 24% (95% CI, 13-37), respectively; DOR, PFS, and OS will be presented. Most common grade 3/4 adverse events (AEs): neutropenia (79%), thrombocytopenia (76%), and anemia (43%). Most common nonhematologic grade 3/4 AEs: pneumonia (10%) and hypophosphatemia (5%). AEs led to melflufen dose reduction and discontinuation in 27% and 22% of patients, respectively. Most common serious AEs were pneumonia (9%) and febrile neutropenia (5%). No treatment-related deaths. Melflufen plus dexamethasone showed clinically meaningful efficacy with a manageable safety profile in heavily pretreated RRMM, including in patients with TCR disease and EMD.

Background: Patients with RRMM receive multiple lines of therapy in their disease course and often become refractory to or are intolerant of newer approved therapies (eg, IMiDs, anti-CD38 monoclonal antibody [mAb] therapy, proteasome inhibitors [PIs]), limiting effective treatment options (Kumar et al. Leukemia. 2017; 31:2443). Efficacy outcomes decrease with each line of therapy, showing a need for agents with novel mechanisms of action to improve treatment responses and survival outcomes (Gandhi et al. Leukemia. 2019;33:2266). Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. In the phase 2 HORIZON study (OP-106; NCT02963493), melflufen plus dexamethasone demonstrated encouraging efficacy in heavily pretreated patients with RRMM refractory to pomalidomide and/or an anti-CD38 mAb (overall response rate [ORR], 29%; median progression-free survival [PFS], 4.2 months; median overall survival [OS], 11.6 months) with a clinically manageable safety profile characterized primarily by hematologic adverse events (Richardson et al. EHA 2020. Abs. EP945). A contemporary representative control cohort is often used to indirectly compare outcomes of patients in clinical trials versus real-world data. The retrospective MAMMOTH study investigated the natural history and outcomes of patients with RRMM refractory to anti-CD38 mAb therapy after treatment with conventional agents (Gandhi et al. Leukemia. 2019;33:2266), providing a benchmark for the evolving state of the RRMM treatment landscape. Outcomes in clinical studies of novel agents in RRMM have been compared with MAMMOTH previously (Costa et al. ASH 2019. Abs. 3125), but not specifically in patients with RRMM refractory to anti-CD38 mAb therapy. To contextualize the clinical benefit of melflufen plus dexamethasone compared with conventional agents for patients with RRMM refractory to anti-CD38 mAb therapy, an analysis was conducted evaluating efficacy outcomes in HORIZON versus MAMMOTH. Methods: HORIZON patients with RRMM refractory to anti-CD38 mAb in the last line of therapy in the intention-to-treat population at final analysis (data cutoff date, 14 Jan 2020) were included in this analysis (N=63). Patients received melflufen 40 mg (intravenously on day 1 of each 28-day cycle) plus dexamethasone 40 mg weekly until disease progression or unacceptable toxicity. The MAMMOTH dataset included patients who progressed while on anti-CD38 mAb therapy (N=275) and were subsequently treated (N=249). ORR was assessed by the investigator per the International Myeloma Working Group criteria. PFS was defined as the time between the first dose of therapy and disease progression or death. OS was defined as the time from refractoriness to anti-CD38 mAb therapy to death from any cause in contrast to clinical studies in which OS is generally measured from first dose of subsequent therapy. Results: Patients in HORIZON and MAMMOTH had similar baseline median age and profile of daratumumab and isatuximab refractoriness (Table). Patients in HORIZON were more heavily pretreated than those in MAMMOTH (median number of prior therapies [range], 5 [2-10] versus 4 [1-16]). Patients in MAMMOTH were often treated with triplet therapy as first subsequent therapy after anti-CD38 mAb therapy failure (Table). ORR for HORIZON patients who failed last-line therapy with an anti-CD38 mAb (N=63) was 35% versus 31% for all anti-CD38 mAb therapy-refractory patients who received conventional agents in MAMMOTH. Median PFS was 4.6 months (95% CI, 3.7-6.4) versus 3.4 months (95% CI, 2.8-4.0), and median OS from last line was 15.4 months (95% CI, 12.0-25.6) versus 9.3 months (95% CI, 8.1-10.6) for these patients in HORIZON and MAMMOTH, respectively. Conclusion: This indirect comparison of patients with RRMM refractory to anti-CD38 mAb therapy in HORIZON and MAMMOTH suggests longer survival outcomes with melflufen plus dexamethasone (median PFS and OS of 4.6 and 15.4 months, respectively) versus those with conventional agents, despite HORIZON having more heavily pretreated patients. This analysis underscores the high burden of disease and unmet needs for patients with RRMM and the feasibility of novel combination therapy in this setting. Disclosures Blade Creixenti: Takeda: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Mateos:Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria, Membership on an entity's Board of Directors or advisory committees. Oriol:GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy; Amgen: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Larocca:GSK: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria. Cavo:Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; GlaxoSmithKline: Honoraria, Speakers Bureau; Karyopharm: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Rodríguez-Otero:Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Abbvie: Consultancy; Kite: Consultancy; Sanofi: Consultancy; Celgene/Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Medscape: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; GlaxoSmithKline: Consultancy, Current Employment, Current equity holder in publicly-traded company; Oncopeptides: Consultancy. Leleu:GSK: Honoraria; Sanofi: Honoraria; Novartis: Honoraria; Carsgen: Honoraria; Incyte: Honoraria; Merck: Honoraria; Amgen: Honoraria; Karyopharm: Honoraria; AbbVie: Honoraria; BMS-celgene: Honoraria; Janssen: Honoraria; Oncopeptide: Honoraria. Nadeem:Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Adaptive: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Hassoun:Novartis: Consultancy; Celgene: Research Funding; Takeda: Research Funding. Touzeau:Abbvie: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding; Amgen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; GlaxoSmithKline: Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Sanofi: Honoraria, Research Funding. Amor:Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene-BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; GSK: Membership on an entity's Board of Directors or advisory committees. Maisel:Takeda: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Karyopharm: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Celgene: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau. Mazumder:The Oncology Institute: Current Employment; Amgen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau. Raptis:INTEGRA: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; UPMC: Current Employment. Puig:BRISTOL-MYERS SQUIBB: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; AMGEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; CELGENE: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; JANSSEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; TAKEDA: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; THE BINDING SITE: Consultancy, Honoraria. Zavisic:Oncopeptides AB: Current Employment, Current equity holder in publicly-traded company. Thuresson:Oncopeptides: Consultancy, Current equity holder in publicly-traded company; Statisticon: Current Employment. Harmenberg:Oncopeptides AB: Consultancy, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Medivir AB: Current equity holder in publicly-traded company; Ultupharma AB: Current equity holder in private company. Richardson:Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. OffLabel Disclosure: This is an indirect comparison of clinical studies, including a phase 2 investigational study of melflufen in RRMM

Background: Current treatments for MM consist of multidrug regimens combining a variety of drug classes including IMiDs, proteasome inhibitors (PIs), monoclonal antibodies (mAbs), alkylators, XP01 inhibitors, histone deacetylase inhibitors, and corticosteroids. Despite advances in therapy, outcomes remain poor for pts with RRMM. Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. In the pivotal, phase 2 HORIZON study (NCT02963493), melflufen plus dex showed meaningful efficacy and a safety profile characterized primarily by clinically manageable hematologic adverse events (AEs) in heavily pretreated and poor-risk pts with RRMM (Richardson et al. EHA 2020. Abs. EP945). Preclinical data show that melflufen is 50-fold more potent than melphalan against MM cells due to an increased intracellular alkylator concentration (Wickstrom et al. Oncotarget. 2017;8:666641). Melflufen has a mechanism of action distinct from alkylators, with cytotoxicity independent of p53 activity (Slipicevic et al. AACR 2020. Abs. 1843). In this analysis, the clinical activity of melflufen is examined in a subset of pts exposed to prior alkylator therapy. Methods: Pts with RRMM had received ≥2 prior lines, including an IMiD and PI, and were refractory to pomalidomide and/or an anti-CD38 mAb. Pts received melflufen 40 mg on d1 of each 28-d cycle plus dex 40 mg/wk until progressive disease or unacceptable toxicity. The primary endpoint was overall response rate (ORR; ≥ partial response [PR]; assessed by the investigator per International Myeloma Working Group criteria). Secondary endpoints included duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Refractoriness was defined as disease that failed to achieve a minimal response or progressed while on primary or salvage therapy or progressed within 60 d of last therapy. Results: Of 157 pts included (data cutoff date, Jan 14, 2020), 138 (88%) had been exposed to and 92 (59%) were refractory to prior alkylator therapy. Baseline characteristics for pts refractory to prior alkylators were generally consistent with those of the overall population apart from more advanced International Staging System score (ISS 3, 34% and 25%), number of prior lines of therapy (6 and 5), and triple-class-refractoriness (83% and 76%). As in the overall population, a high proportion of pts refractory to alkylators had high-risk cytogenetics (40%) and extramedullary disease (36%), representing a difficult-to-treat group. Overall, 60% of pts refractory to alkylators had been exposed to (median time since last exposure, 1.3 y) and 27% were refractory to an alkylator in ≥1 line, and 22% were refractory to an alkylator in the last line. The ORR (95% CI) was 20.7% (12.9-30.4) in pts refractory to prior alkylators and 29.3% overall (Table). Among responding pts refractory to prior alkylators (n=19), 1 achieved a stringent complete response, 6 a very good PR, and 12 a PR. Median DOR (95% CI) was 4.2 mo (3.2-7.6) in pts refractory to prior alkylators and 5.5 mo (3.9-7.6) overall. Median PFS (95% CI) was 3.7 mo (3.0-4.5) and 4.2 mo (3.4-4.9), respectively, and OS was 9.7 mo (6.2-13.2) and 11.6 mo (9.3-15.4), respectively, in pts refractory to prior alkylators and overall. ORR (95% CI) was 20.0% (10.0-33.7) and 21.4% (10.3-36.8) in pts who had received alkylator treatment for <6 mo and >6 mo, respectively; ORR in pts exposed to melphalan was 26.3% (95% CI, 16.9-37.7). The safety profile of melflufen plus dex in pts refractory to prior alkylators was consistent with that in the overall population. In pts refractory to prior alkylators and the overall population, grade 3/4 AEs were reported in 91% and 89% of pts, respectively most commonly thrombocytopenia (61% and 57%), neutropenia (57% and 53%), and anemia (43% and 43%). The most common nonhematologic AE was pneumonia (11% and 10%). Serious AEs occurred in 55% of pts refractory to prior alkylators and 49% of pts overall; most commonly pneumonia (9% and 9%) and febrile neutropenia (7% and 5%). Conclusion: Melflufen has a distinct mechanism of action from that of melphalan and other alkylators and in combination with dex showed efficacy in pts with disease refractory to prior alkylator therapy with a manageable safety profile. These results are consistent with those of previous preclinical and clinical studies. Disclosures Rodríguez-Otero: Janssen, BMS: Other: Travel, accommodations, expenses; Celgene-BMS: Consultancy, Honoraria; Mundipharma: Research Funding; BMS, Janssen, Amgen: Honoraria; Janssen, BMS, AbbVie, Sanofi, GSK, Oncopeptides, Kite, Amgen: Consultancy, Honoraria. Mateos:Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Oriol:Janssen: Consultancy; Sanofi: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees. Larocca:Amgen: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees; GSK: Honoraria; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Blade Creixenti:Janssen: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Cavo:AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Karyopharm: Honoraria; GlaxoSmithKline: Honoraria, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Leleu:AbbVie: Honoraria; Novartis: Honoraria; Amgen: Honoraria; GSK: Honoraria; Sanofi: Honoraria; Oncopeptide: Honoraria; Karyopharm: Honoraria; Incyte: Honoraria; Merck: Honoraria; BMS-celgene: Honoraria; Janssen: Honoraria; Carsgen: Honoraria. Nadeem:Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Amgen: Membership on an entity's Board of Directors or advisory committees; Adaptive: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Hassoun:Novartis: Consultancy; Celgene: Research Funding; Takeda: Research Funding. Touzeau:Amgen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; GlaxoSmithKline: Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Sanofi: Honoraria, Research Funding. Amor:Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene-BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Maisel:Takeda: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Amgen: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Celgene: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau. Mazumder:Takeda: Honoraria, Speakers Bureau; The Oncology Institute: Current Employment; Celgene: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau. Raptis:INTEGRA: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; UPMC: Current Employment. Puig:JANSSEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; TAKEDA: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; AMGEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; CELGENE: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; BRISTOL-MYERS SQUIBB: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; THE BINDING SITE: Consultancy, Honoraria. Thuresson:Statisticon: Current Employment; Oncopeptides: Consultancy, Current equity holder in publicly-traded company. Harmenberg:Ultupharma AB: Current equity holder in private company; Medivir AB: Current equity holder in publicly-traded company; Oncopeptides AB: Consultancy, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Harlin:Oncopeptides AB: Consultancy, Current equity holder in publicly-traded company. Richardson:Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. OffLabel Disclosure: This is a phase 2 investigational study of melflufen in RRMM.

Context: Outcomes in RRMM remain poor (Kumar et al. Leukemia. 2017; 31:2443), and treatment options are limited for RRMM refractory to multiple drug classes (Gandhi et al. Leukemia. 2019; 33:2266). Melphalan flufenamide (melflufen) is a first-in-class anticancer peptide-drug conjugate that rapidly delivers an alkylating payload into tumor cells. A phase 1/2 study established the dosage of melflufen plus dexamethasone in RRMM (Richardson et al. Lancet Haematol. 2020; 7:e395). Objective: Evaluate the efficacy and safety of melflufen plus dexamethasone in RRMM in the pivotal, single-arm, multicenter, phase 2 HORIZON study ( NCT02963493 ). Methods: Patients who had RRMM, ≥2 prior lines of therapy (≥1 IMiD + ≥1 proteasome inhibitor [PI]), and were refractory to pomalidomide and/or an anti-CD38 mAb received melflufen plus dexamethasone until progressive disease or unacceptable toxicity. Primary endpoint: overall response rate (ORR; investigator-assessed per IMWG criteria). Secondary endpoints: duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Subgroup analyses: triple-class–refractory (TCR) disease (refractory to or intolerant of ≥1 IMiD + ≥1 PI + ≥1 anti-CD38 mAb) and extramedullary disease (EMD). Results: Of 157 patients treated (intention-to-treat [ITT]); 26 remain on study (data cutoff: January 14, 2020). Median age: 65 years (range, 35-86); 25% had ISS stage III disease; and 35% had EMD. Median prior lines of therapy: 5 (range, 2-12); 76% had TCR disease. In the ITT, ORR was 29% (95% CI, 22-37); median (95% CI) DOR was 5.5 months (3.9-7.6); PFS was 4.2 months (3.4-4.9); and OS was 11.6 months (9.3-15.4). In patients with TCR disease and EMD, ORR was 26% (95% CI, 18-35) and 24% (95% CI, 13-37), respectively; DOR, PFS, and OS will be presented. Most common grade 3/4 adverse events (AEs): neutropenia (79%), thrombocytopenia (76%), and anemia (43%). Most common nonhematologic grade 3/4 AEs: pneumonia (10%) and hypophosphatemia (5%). AEs led to melflufen dose reduction and discontinuation in 27% and 22% of patients, respectively. Most common serious AEs were pneumonia (9%) and febrile neutropenia (5%). No treatment-related deaths. Conclusion: Melflufen plus dexamethasone showed clinically meaningful efficacy with a manageable safety profile in heavily pretreated RRMM, including in patients with TCR disease and EMD.

e20570 Background: Melflufen is a novel peptide-drug conjugate that rapidly delivers a cytotoxic payload into tumor cells. Melflufen + dex showed efficacy and a manageable safety profile in pts with poor-risk, heavily pretreated RRMM in the phase 2 HORIZON study (Mateos et al. ASH 2019. Abs. 1883). For pts with RRMM, longer TTNT is indicative of disease stabilization and clinical benefit and is associated with lower costs (Chen et al. J Manag Care Spec Pharm. 2017). This report of TTNT after melflufen + dex from HORIZON is, to our knowledge, the first report from a trial population with such advanced RRMM. Methods: Pts with RRMM who had received ≥2 prior lines of therapy, including an IMiD and a proteasome inhibitor (PI), and were refractory to pomalidomide and/or an anti-CD38 monoclonal antibody (mAb), received melflufen 40 mg (IV on d1 of each 28-d cycle) + dex 40 mg/wk until disease progression or unacceptable toxicity. The primary endpoint was overall response rate. Secondary endpoints included progression-free survival (PFS) and safety. TTNT was defined as the time from start of melflufen + dex to first subsequent therapy. Results: Overall, 154 pts were treated (data cutoff, Oct 1, 2019); median age was 64.5 y (range, 35-86), 32% had International Staging System stage 3 disease, 38% had high-risk cytogenetics, 32% had extramedullary disease (EMD), the median number of prior therapies was 5 (range, 2-12), and 71% had triple-class refractory MM (IMiD + PI + anti-CD38 mAb). Treatment discontinuation occurred in 108 pts (70%), most commonly due to disease progression (47%) and adverse events (14%). Among 125 pts evaluable for response, with a median follow up of 15.3 mo, the median TTNT was 8.0 mo (95% CI, 7.2-8.9) and the median PFS was 4.2 mo (95% CI, 3.7-4.9). TTNT and PFS were similar in subgroups of pts with triple-class refractory MM and EMD (Table). Subsequent therapies after melflufen + dex will be presented. Conclusions: TTNT in HORIZON (median 5 prior lines) was consistent with previous reports of TTNT in pts with RRMM who received melflufen + dex or other therapies (median 2-4 prior lines) (Bringhen et al. J Clin Oncol. 2019. Abs. 8043). Melflufen + dex is being further evaluated in the phase 3 OCEAN study (NCT03151811) in pts with RRMM who are refractory to lenalidomide. Clinical trial information: NCT02963493. [Table: see text]

Background: With advances in therapy, outcomes have generally improved for pts with MM; however, pts with late-stage RRMM have limited treatment options and poor outcomes (Kumar et al. Leukemia. 2017;31:2443; Gandhi et al. Leukemia. 2019;33:2266). Pts with late-stage RRMM, often older and having comorbidities, require efficacious and tolerable therapies to maintain HRQoL (Richardson et al. Blood. 2019;134[suppl 1]:3487). Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. In the pivotal, phase 2, HORIZON study (NCT02963493) melflufen plus dex showed an overall response rate of 29%, median progression-free survival of 4.2 months, median overall survival of 11.6 months, and a manageable safety profile (N=157; Richardson et al. EHA 2020. Abs EP945). A previous baseline (BL) HRQoL analysis concluded that the HORIZON population is representative of RRMM populations, with a poor overall HRQoL relative to other populations with advanced cancers (Richardson et al. ASH 2019. Abs 3487). This analysis evaluates HRQoL in pts with RRMM throughout treatment with melflufen plus dex in the HORIZON study. Methods: Eligible pts received melflufen 40 mg on d1 of each 28-day cycle plus dex 40 mg/wk (20 mg in pts aged ≥75 y). HRQoL was added as a secondary endpoint as an amendment to the HORIZON protocol, which allowed collection of data from a subset of pts using the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 V.3 (EORTC QLQ-C30) and the EuroQOL 5 Dimension-3 Level (EQ-5D) questionnaires. EORTC QLC-C30 evaluates functional domains and symptoms on a scale from 0-100 (higher functional scores = better function; higher symptom scores = more symptomatology/problems). The EQ-5D index is evaluated on a scale from 0 (death) to 1 (perfect health) and the EQ-5D VAS is evaluated on a scale from 0 (death) to 100 (perfect health). Questionnaires were administered before dosing at BL (cycle [C] 1) and predose at intervals throughout the study. Descriptive data for pts with post-BL assessments at C2, C4, and C6 are presented herein. Pts with only BL questionnaire assessments were excluded from this analysis. Select EORTC QLQ-C30 and EQ-5D results are presented. This analysis is ongoing. Results: At HRQoL data cutoff (May 28, 2020), of the 64 pts with post-BL HRQoL assessments, 19 remained on therapy. Among 64 pts in the HRQoL subgroup, median age was 67 y (range, 46-84); 17% had International Staging System stage 3 disease; and 36% had high-risk cytogenetics at study entry. Pts had received a median of 5 prior lines of therapy (range, 2-10). At C2, C4, and C6, 97.9%, 98.9%, and 99.4% of pts with ongoing treatment completed HRQoL assessments. Mean EORTC QLQ-C30 summary score and mean EQ-5D scores were relatively constant from BL through C6 (Figure). EORTC QLQ-C30 global health status/QoL and emotional functioning had mean scores of 58.6 and 78.4, respectively, at BL and 63.0 and 83.7, respectively, at C6 (Table). Mean symptom scores at BL and C6 for pain were 39.1 and 29.0, respectively, and for fatigue were 39.4 and 38.2, respectively. The EQ-5D VAS and EQ-5D index scores were generally consistent throughout treatment, with mean scores of 61.4 and 0.75, respectively, at BL and 62.3 and 0.74, respectively, at C6. Among pts with HRQoL data and the overall population (n=64 and N=157, respectively; Jan 14, 2020 data cutoff date), 92% and 89% had ≥1 grade 3/4 AEs, respectively; most common AEs were white blood cell count decreased (42% and 26%), thrombocytopenia (41% and 57%), and anemia (39% and 43%); most common nonhematologic grade 3/4 AEs was pneumonia (14% and 10%). SAEs occurred in 47% of pts in the HRQoL group and 49% of patients overall, most commonly pneumonia (14% and 9%); there were no treatment-related deaths. Conclusion: The EORTC QLQ-C30 global health status/QoL score and EQ-5D VAS and index scores were consistent from BL throughout treatment, suggesting that melflufen plus dex preserves HRQoL in pts with RRMM. The safety profile of melflufen plus dex consisted primarily of clinically manageable hematologic AEs in the overall pt population. No new safety signals were observed in the HRQoL-evaluable population. These findings are encouraging as treatment-related AEs may negatively affect HRQoL in RRMM. Data should be interpreted with caution due to the attrition of pts over time. Disclosures Oriol: Sanofi: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Janssen: Consultancy. Richardson:Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. Mateos:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees. Larocca:Amgen: Honoraria; GSK: Honoraria; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Blade Creixenti:Amgen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees. Cavo:GlaxoSmithKline: Honoraria, Speakers Bureau; Karyopharm: Honoraria; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Rodríguez-Otero:Abbvie: Consultancy; Kite: Consultancy; Amgen: Honoraria; Medscape: Membership on an entity's Board of Directors or advisory committees; Celgene/Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Sanofi: Consultancy; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Oncopeptides: Consultancy; GlaxoSmithKline: Consultancy, Current Employment, Current equity holder in publicly-traded company. Nadeem:Adaptive: Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Amgen: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Hassoun:Novartis: Consultancy; Celgene: Research Funding; Takeda: Research Funding. Touzeau:Amgen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Takeda: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; GlaxoSmithKline: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding; Sanofi: Honoraria, Research Funding. Amor:Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene-BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees. Maisel:Incyte: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Amgen: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Celgene: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau. Mazumder:Takeda: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; The Oncology Institute: Current Employment. Raptis:INTEGRA: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; UPMC: Current Employment. Puig:AMGEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; TAKEDA: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; BRISTOL-MYERS SQUIBB: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; JANSSEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; CELGENE: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; THE BINDING SITE: Consultancy, Honoraria. Strang:Karolinska Institutet: Current Employment; Oncopeptides: Consultancy. Sandberg:Novo Nordisk AS: Divested equity in a private or publicly-traded company in the past 24 months, Ended employment in the past 24 months; Oncopeptides AB: Current Employment. Jaques:Pfizer: Consultancy; Morphosys AG: Consultancy; Oncopeptides: Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Pharma Biotech Consultants: Consultancy; Oncopeptides: Ended employment in the past 24 months. Thuresson:Oncopeptides: Consultancy, Current equity holder in publicly-traded company; Statisticon: Current Employment. Orre:Oncopeptides: Current Employment. Leleu:GSK: Honoraria; Novartis: Honoraria; Amgen: Honoraria; Sanofi: Honoraria; Janssen: Honoraria; AbbVie: Honoraria; Oncopeptide: Honoraria; Karyopharm: Honoraria; Carsgen: Honoraria; Incyte: Honoraria; Merck: Honoraria; BMS-celgene: Honoraria. OffLabel Disclosure: This is a phase 2 investigational study of melflufen in RRMM.

Background: Recent advances have improved survival in multiple myeloma (MM; Kumar et al. Leukemia. 2014); however, the disease remains incurable. Patients with triple-class refractory MM have a median overall survival (OS) of only 9.2 months (Ghandi et al. Leukemia. 2019). These patients and those with poor-risk features, such as high-risk cytogenetics, have few treatment options and represent a patient group with a very poor prognosis and high unmet medical need. Melflufen is a lipophilic peptide-conjugated alkylator that rapidly delivers a highly cytotoxic payload into myeloma cells through peptidase activity. Meflufen is taken up by myeloma cells and immediately cleaved by peptidases into hydrophilic alkylator payloads that induce irreversible DNA damage and apoptosis. This updated analysis of the ongoing HORIZON study in patients with MM refractory to pomalidomide (pom) and/or daratumumab (dara) includes a subgroup analysis of patients with triple-class refractory (no response or progression on or within 60 days of last dose to at least 1 IMiD, 1 proteasome inhibitor [PI], and 1 anti-CD38 monoclonal antibody) and high-risk cytogenetics at baseline (NCT02963493). Methods: Patients with relapsed refractory MM (RRMM) must have received ≥2 prior lines, been exposed to an IMiD and PI, and be refractory to pom and/or dara. Patients receive 40-mg melflufen intravenously on day 1 of each 28-day cycle and 40-mg weekly dexamethasone (dex; 20 mg for patients aged ≥75 years) until progressive disease (PD) or unacceptable toxicity. The primary endpoint is overall response rate (ORR; ≥ partial response [PR]; investigator assessed per International Myeloma Working Group criteria). Secondary endpoints include safety, clinical benefit rate (CBR; ≥ minimal response), progression-free survival (PFS), OS, and duration of response (DOR). Results: As of 6 May 2019, 121 patients were treated. The median age was 64 years (range, 35-86), median time since diagnosis was 6.2 years (range, 0.7-25), 29% of patients had International Staging System stage 3 disease, and 62% with available cytogenetic data (n=81) had high-risk cytogenetics at study entry. The median number of prior lines was 5 (2-12). All patients were pom or dara refractory and received prior PIs and IMiDs; 74% were triple-class refractory. With a median follow-up of 10.8 months, 29% of patients were on ongoing treatment. Of 86 patients (71%) who discontinued treatment, 69% discontinued due to PD, 20% due to adverse events (AEs), and 12% for other reasons. In total, 113 patients had available response data. ORR was 28%; 1 patient achieved stringent complete response (sCR), 9% very good PR (VGPR), and 19% PR. CBR was 40%. Median PFS for all patients treated (N=121) was 4.0 months (95% CI, 3.7-4.6), median OS was 11.2 months (95% CI, 8.1-13.9), and median DOR was 4.4 months (95% CI, 3.6-8.3). Efficacy was examined in poor-risk patient subsets with available response data. ORR was 20% in patients with triple-class refractory disease (n=83). ORR in patients with high-risk cytogenetics was 28%. Median DOR was 3.6 months in responders with triple-class refractory disease. DOR in patients with high-risk cytogenetics was 5.1 months. Treatment-related grade 3 and grade 4 AEs were reported in 24% and 49% of patients, respectively. Most common (≥5%) grade 4 AEs were thrombocytopenia (36%) and neutropenia (31%). The incidence of treatment-related grade 3/4 nonhematologic AEs was low; most commonly pneumonia (3%), fatigue (2%), and upper respiratory tract infection (2%). Treatment-related serious AEs occurred in 20% of patients. No treatment-related deaths were reported. Conclusion: Melflufen continues to show promising activity (ORR, 28%) in patients with late-stage RRMM refractory to dara and/or pom and was generally well tolerated, with infrequent nonhematologic AEs and, of the 121 patients treated, 14% discontinued due to AEs. Additionally, melflufen has comparable efficacy in subsets of patients with poor-risk features, including triple-class refractory and high-risk cytogenetics, relative to the overall HORIZON patient population. Melflufen plus dex is being further investigated vs pom plus dex in the OCEAN phase 3 study (OP-103; NCT03151811) in patients with RRMM refractory to lenalidomide. Disclosures Mateos: Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; EDO: Membership on an entity's Board of Directors or advisory committees; Pharmamar: Membership on an entity's Board of Directors or advisory committees. Oriol:Janssen: Consultancy; Takeda: Consultancy, Speakers Bureau; Celgene Corporation: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau. Larocca:Amgen: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Rodriguez Otero:Kite Pharma: Consultancy; BMS: Honoraria; Celgene Corporation: Consultancy, Honoraria, Speakers Bureau; Takeda: Consultancy; Janssen: Consultancy, Honoraria. Bladé:Jansen, Celgene, Takeda, Amgen and Oncopeptides: Honoraria. Cavo:AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; novartis: Honoraria; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hassoun:Celgene: Research Funding; Janssen: Research Funding; Novartis: Consultancy. Leleu:Sanofi: Honoraria; Oncopeptide: Honoraria; Takeda: Honoraria; Karyopharm: Honoraria; Amgen: Honoraria; Carsgen: Honoraria; Incyte: Honoraria; Novartis: Honoraria; Celgene: Honoraria; Janssen: Honoraria; BMS: Honoraria; Merck: Honoraria. Amor:Takeda: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Maisel:Texas Oncology: Employment; Amgen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Gilead: Honoraria, Speakers Bureau; Verastem: Honoraria, Speakers Bureau. Paner:Amgen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Cellectar: Consultancy, Honoraria; Dova: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Oncopeptides: Consultancy, Honoraria; Rush University Medical Center: Employment; Cellectar: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Harmenberg:Oncopeptides: Consultancy, Equity Ownership. Byrne:Oncopeptides: Consultancy; Takeda: Consultancy. Thuresson:Oncopeptides: Employment, Equity Ownership. Zubair:Oncopeptides: Employment, Equity Ownership. Richardson:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees. OffLabel Disclosure: This is a phase 2 investigational study of melflufen in RRMM

Background: Melflufen is an alkylating peptide belonging to a novel class of peptidase-enhanced compounds. Aminopeptidases are heavily overexpressed and key for the transformation process in multiple myeloma (MM). Melflufen selectively targets MM through aminopeptidase-driven accumulation, leading to a 50-fold enrichment of alkylating metabolites vs melphalan (Chauhan et al. Clin Can Research. 2013). In the Phase I/II O-12-M1 study, melflufen showed activity in pts with RRMM (overall response rate [ORR], 31%; median progression-free survival [PFS], 5.7 mo; median overall survival, 20.7 mo), with acceptable safety (Richardson et al. Blood. 2017). The Phase II HORIZON study evaluates melflufen in pts exposed to IMiDs and proteasome inhibitors (PIs) and refractory to pom and/or dara. Methods: Pts with RRMM must have received ≥2 prior lines of therapy and have been exposed to IMiDs and PIs and refractory to pom and/or dara. Pts receive 40 mg melflufen intravenously on Day 1 of each 28-day cycle + 40 mg weekly dexamethasone. The primary endpoint is ORR (≥ partial response; investigator assessed per International Myeloma Working Group criteria). Secondary endpoints include clinical benefit rate (CBR; ≥ minimal response), PFS, and safety. Pts are treated until progressive disease (PD) or unacceptable toxicity. Results: As of 22 Oct 2018, 83 pts were treated. Median age was 63 y (35-86), median time since diagnosis was 6.5 y (0.75-25); 36% of pts were International Staging System (ISS) stage 3 and 61% had high-risk cytogenetics at study entry. Median no. of prior lines was 5 (2-13). All pts were pom or dara refractory, 60% were pom and dara refractory and 86% were double refractory (IMiD and PI). Also, 84% had received prior alkylator therapy (55% alkylator refractory); 69% had received ≥1 prior transplant. Treatment was ongoing for 23% of pts and discontinued in 77% of pts due to PD (57%), adverse event (AE; 13%), or other (7%). Treatment-related grade 3/4 AEs were reported in 62 (75%) pts, mostly hematologic: neutropenia (61%), thrombocytopenia (59%), and anemia (25%). Treatment-related non-hematologic grade 3/4 AEs were rare (eg, infections in 7% of pts). Fourteen (16%) pts experienced treatment-related serious AEs, most commonly febrile neutropenia (n=5), neutropenia (n=3), and thrombocytopenia (n=2). No treatment-related deaths were reported. In total, 82 pts were evaluable for response: ORR was 33% and CBR 39%. Benefit was observed for high-risk subgroups: ORR for pts with ISS stage 3, high-risk cytogenetics, and double- and dara-refractory disease was 24%, 22%, and 19%, respectively. Median PFS was 4.0 mo (95% CI, 3.3-5.1). Conclusion: Melflufen has promising activity in heavily pretreated, multi-refractory late-stage pts with RRMM. Melflufen was generally well tolerated with infrequent non-hematologic AEs and low rates of discontinuation due to AEs. Citation Format: Paul G. Richardson, Albert Oriol, Alessandra Larocca, Paula Rodriguez Otero, Jan Moreb, Joan Bladé, Hani Hassoun, Michele Cavo, Adrián Alegre, Amitabha Mazumder, Christopher Maisel, Agne Paner, Xavier Leleu, Jeffrey A. Zonder, Johan Harmenberg, Sara Thuresson, Hanan Zubair, María-Victoria Mateos. Melflufen in patients (pts) with relapsed/refractory multiple myeloma (RRMM) refractory to daratumumab (dara) and/or pomalidomide (pom) (OP-106) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT154.