Abstract Background: Standardized definitions of efficacy endpoints are needed to improve clinical trial designs, data reporting and interpretation of results, and to allow cross-trial comparisons. STEEP (Standardized Definitions for Efficacy Endpoints) criteria were proposed in 2007 by an expert panel from the National Cancer Institute (NCI) to provide common definitions for clinical trials in early breast cancer (BC). Invasive disease-free survival (IDFS) was selected as a candidate surrogate endpoint for overall survival (OS) in adjuvant trials and has been widely used in the last 15 years. Advances in BC systemic treatment led to review these criteria (STEEP v2.0), with the definition of a new modified endpoint: invasive BC-free survival (IBCFS). IBCFS excludes second primary non-breast invasive cancers from IDFS which may better detect efficacy effects when the toxicity profile of the intervention is well-known and the risk of second primary cancer is small. Methods: We proposed a multi-trial analysis of 8 adjuvant chemotherapy (CT) trials from GEICAM and TRIO to evaluate the different surrogate endpoints defined in the STEEP v2.0. Trial-level surrogacy was assessed through correlation between the ln hazard ratio (HR) of OS and the ln HR of the different studied endpoints across trials. The correlation was estimated by the weighted, by trial size, least squares regression (WLS) line and evaluated comparing the R2 values between OS and the corresponding endpoint tested. Primary analyses evaluated the correlation of OS with IDFS/IBCFS. Secondary analyses evaluated the correlation of OS with other STEEP v2.0 endpoints (distant disease-free survival [DDFS], distant relapse-free survival [DRFS], recurrence-free survival [RFS], recurrence-free interval [RFI] and distant recurrence-free interval [DRFI]) and explored the surrogacy between OS and all endpoints in specific groups of patients (pts) according to their risk of relapse: hormone receptors positive (HR+)/HER2-negative (HER2-) pts with intermediate/high and high-risk and triple negative (TN) pts. Results: A total of 14,473 pts were included. Median age was 50 years (range, 20–82). All were female, and 51.8% were postmenopausal. With a median follow-up of 115 months (range, 0.0–188) we found 2,504 OS events, 4,146 IDFS events (60.9% being distant recurrences) and 3,810 IBCFS events (62.4% being distant recurrences). For each trial, HR of OS, IDFS and IBCFS indicated same conclusions. If HR< 1 for OS, it was also for IDFS and IBCFS and the same was true when HR >1. R2 results of the weighted linear correlations between the ln HR of OS versus (vs) IDFS and OS vs IBCFS were 0.86 and 0.89, respectively. Confidence intervals (CI) at 95% were both overlapping. All other efficacy endpoints showed strong correlation with OS in the overall analysis. R2 values for HR+/HER2- intermediate/high and high-risk pts were 0.89 (OS vs IDFS) and 0.84 (OS vs IBCFS). For TN pts the correlations were weaker, being 0.63 (OS vs IDFS) and 0.73 (OS vs IBCFS). All WLS R2 values are described in the table. Conclusions: All tested STEEP v2.0 endpoints were strongly correlated with OS (R2 close to 1), meaning that their use as surrogate endpoints for adjuvant CT trials is appropriate. Notably, no differences were found between them in this multi-trial analysis. Therefore, none of them is more appropriate than other to discriminate the value of a new intervention vs comparator in adjuvant CT studies with mature data and long-term follow-up. Table: Citation Format: Sara López-Tarruella, Marina Pollan, Ander Urriticoechea, Eva Carrasco, Gonzalo Spera, Miguel Martín, Begoña Bermejo, Linnea Chap, Manuel Ruíz - Borrego, John Crown, Jose Angel García-Sáenz, Arlene Chan, Angel Guerrero, Valerie Bee, Lourdes Calvo, Rodrigo Fresco, Andrea Blasco, Andrés Hernando, Dennis Slamon. STEEP criteria v2.0 validation: A multi-trial analysis using GEICAM and TRIO adjuvant trials to evaluate surrogate endpoints for overall survival [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-03-03.

Background: De novo and acquired resistance to HER2 directed therapy is frequently encountered. Upregulation of the phosphatidylinositol-3-kinase (PI3K) pathway is an important mediator of treatment resistance. This can occur through an activating mutation of the PIK3CA gene or PTEN loss. PIK3CA mutations are present in approximately 20% of HER2 positive breast cancers and as such, the PI3K pathway has emerged as an attractive target for restoring sensitivity to HER2 directed therapy. Methods: We performed a single arm, multicentre, open label Phase Ib/II trial. Patients (pts) with advanced HER2-positive breast cancer whose disease had progressed on at least 1 line of Trastuzumab/T-DM1 based treatment in the metastatic setting were eligible if they met following criteria: ECOG PS ≤ 2 and adequate organ function. Pts with treated, controlled brain metastases were permitted to enrol. Exclusion criteria included uncontrolled hypertension or diabetes mellitus. Pts on Phase IB were treated according to a 6+6 study design with a dose escalation schedule of Copanlisib IV (level 1 = 45mg, level 2 = 60mg) on Day 1, 8 and 15 of a 28-day cycle along with a fixed dose of Trastuzumab 2mg/kg weekly. Phase II treatment was the MTD (maximum tolerated dose) of Copanlisib in combination with Trastuzumab. Archival tumour tissue, voluntary biopsies and serial plasma samples were collected for genomic sequencing. Primary endpoints were MTD (Phase I) and clinical benefit rate (CBR) which was defined as complete response (CR) or partial response (PR) at any time point; or stable disease (SD) lasting at least 24 weeks (Phase II). Secondary endpoints included safety and tolerability, tumor response rate, duration of response, time to treatment failure (TTF) and progression free (PFS) and overall survival (OS). Results: Twelve pts were enrolled in Phase IB. No dose limiting toxicity was observed. The MTD was established as Copanlisib 60mg and Trastuzumab 2mg/kg. Fourteen pts were enrolled in Phase II (6 pts treated at the MTD in Phase IB were included in the final Phase II analysis resulting in a total of 20 pts). The median number of lines of prior treatment in the metastatic setting was 3 (1-8). The most common grade 3-4 toxicities encountered in the Phase Ib/II cohorts included hypertension (n=7, 27%), hyperglycaemia (n=2, 8%) and vomiting (n=2, 8%). Three pts discontinued treatment due to toxicity. The median follow-up for the Phase II cohort was 7.5 months (95% CI 6.0-14.5). PR was observed in 4 pts (20%) and SD (at any time point) was seen in 8 pts (40%). The CBR was 30% (n=6). The duration of response was 15.0 weeks (95% CI 4.9 - 16.1). The median TTF was 11.9 weeks (95% CI 7.5 - 21.1). The median PFS was 3.0 mo (95% CI 0.2 - 5.8) and OS was 14.0 mo (95% CI 5.2-22.8). At the time of analysis, 9 of 20 patients were alive. PIK3CA mutations were detectable in the archival tissue of 11 of 26 pts (42%). PIK3CA hotspot mutations (H1047R, E542K and E545K) were detectable in the plasma of all 26 pts at various points throughout treatment. Pre and post treatment biopsies of 2 pts in the Phase IB trial revealed somatic mutations in DNAH3 and TRRAP, the latter of which encodes a PI3K-like protein kinase. Targeted next generation sequencing was performed on the circulating tumour DNA of 20 pts in the Phase II cohort taken before, during and after treatment to further validate these findings and to assess for other mechanisms of response or resistance. The final translational results will be presented at the meeting. Conclusions: The combination of Copanlisib and Trastuzumab is a safe and tolerable regimen and is associated with clinical efficacy in a heavily pre-treated metastatic HER2-positive breast cancer population. Translational studies may have identified novel resistance biomarkers in this pt cohort. Citation Format: Lisa Prior, Niamh M Keegan, Simon J Furney, Janice M Walshe, Giuseppe Gullo, John Crown, M John Kennedy, Diarmuid Smith, John McCaffrey, Catherine M Kelly, Keith Egan, Jennifer Kerr, Mark Given, Niall Sheehy, Peter O'Donovan, Andres Hernando, Ausra Teiserskiene, Imelda Parker, Elaine Kay, Ray McDermott, Maccon M Keane, Seamus O'Reilly, Liam Grogan, Oscar Breathnach, Patrick G Morris, Sinead Toomey, Bryan T Hennessy. Phase Ib/II trial evaluating safety and efficacy of copanlisib (PI3K inhibitor) and trastuzumab in pre-treated advanced HER2-positive breast cancer: Results from the PantHER study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-16-08.

BACKGROUND:Activation of the phosphoinositide-3 kinase (PI3K) pathway is a resistance mechanism to anti-human epidermal growth factor receptor 2 (HER2) therapy. This phase Ib trial was conducted to determine the maximum tolerated dose (MTD) of copanlisib, an intravenous (IV) pan-class I PI3K inhibitor, combined with trastuzumab.METHODS:Patients with advanced HER2-positive breast cancer and disease progression following at least one prior line of HER2 therapy in the metastatic setting were treated with copanlisib (45 or 60 mg) IV on days 1, 8 and 15 of a 28-day cycle with a fixed dose of trastuzumab 2 mg/kg weekly.RESULTS:Twelve patients were enrolled. The MTD was determined as copanlisib 60 mg plus trastuzumab 2 mg/kg weekly. The most common adverse events of any grade occurring in more than two patients were hyperglycaemia (58%), fatigue (58%), nausea (58%) and hypertension (50%). Stable disease was confirmed at 16 weeks in six participants (50%). PIK3CA mutations were detected in archival tumour of six participants (50%). PIK3CA hotspot mutations, were detectable in pre- and on-treatment plasma of all participants. Pre- and post-treatment tumour biopsies for two patients identified temporal genomic heterogeneity, somatic mutations in the TRRAP gene, which encodes a PI3K-like protein kinase, and emergent somatic mutations related to protein kinase signalling.CONCLUSION:Copanlisib and trastuzumab can be safely administered with fair overall tolerability. Preliminary evidence of tumour stability was observed in patients with heavily pre-treated, metastatic HER2 positive breast cancer. Several potential biomarkers were identified for further study in the current phase 2 clinical trial. NCT: 02705859.

Abstract Background: The addition of H to chemotherapy improved disease outcome in HER2+ MBC. The combination of H and L with chemotherapy improved event free survival (EFS) in the neo-adjuvant setting but not in the adjuvant setting. However, improved EFS did not translate to overall survival benefit. This international trial (ICORG (CTRIAL-IE) 11-10/NCT01526369) compared the efficacy of TH vs. THL in first line treatment of HER2+ MBC. The primary aim of this study was to assess any benefit for the addition of L to TH in an advanced HER2+ breast cancer patient population. Target accrual was not met due to changes to standard of care mid-study. Methods: Patients (Pts) (n= 75 enrolled, randomized 1:1) received weekly T (80mg/m², for 3 weeks of a 4 week cycle) + H (8mg/kg loading dose on cycle 1 day 1 and 4mg/kg every 2 weeks) + L (1,000 mg daily)) until disease progression, unacceptable toxicity or consent withdrawal. The primary outcome measure was progression free survival (PFS). Secondary outcome measure was overall survival (OS). Eligibility criteria included: Female > 18 years, invasive MBC, measurable disease by RECIST criteria V1.1, HER2+ by testing of the primary tumour and if available the biopsied metastatic lesion. No prior systemic therapy for metastatic disease (except one line of hormonal therapy for metastatic disease without H). No recurrence within 12 months (mo) from completion of adjuvant chemotherapy to the development of metastatic disease. No recurrence within 6 mo from completion of adjuvant H to the development of metastatic disease and no prior L treatment. Results: Of the 75 pts enrolled, n=65 (TH n=34, THL n=31) were included in the PFS analysis. Median PFS (95% CI) was numerically higher, but not statistically significant, in THL (24.0 mo (9.5, 34.5)) vs TH (19.3 mo (8.7, 22.7)), HR 0.827, p= 0.601. For OS analysis, n=69 (TH n=35 and THL n=34) were included. 41/69 (59.4%) had no prior therapy. No statistically significant, clinically meaningful improvement in OS (Median (95% CI)) was observed (TH 53.8 mo (41.8, -) vs. THL 45.6 mo (29.7, -), HR 1.048, p=0.891). Analysis of the safety set (n=70 (TH n= 36, THL n=34)) revealed a higher incidence of Grade 3/4 AEs in THL (61.8%) vs. TH (50%), p=0.322. There were 2 on-treatment fatalities due to adverse events (AEs) in the THL arm, one due to respiratory failure, the other due to central nervous system metastasis. There were no on-treatment fatalities in the TH arm. GI disorders were the most prevalent AE, with the incidence of diarrhea significantly higher in the THL arm (88% vs. 42%, p <0.0001). Conclusions: The addition of a HER2-targeted TKI to TH was tolerated with GI toxicity emerging as the predominant AE. While underpowered, this study indicates a numerical advantage in PFS that does not reach statistical significance for the addition of L to TH. This may indicate that the addition of a HER2-targeted TKI to H-containing chemotherapy regimens warrants investigation in HER2+ MBC. Citation Format: John Crown, William Jacot, Denis M. Collins, Linda Coate, Anna Saetersdal, M John Kennedy, Catherine Kelly, Blanca Cantos Sanchez De Ibarguen, Raquel Andrés Conejero, Luis Costa, Margarida Brito, Maccon Keane, Pedro Sanchez Rovira, Miguel Martin, Miriam O'Connor, Manuel Ramos Vazquez, Elena Alvarez, Seamus O'Reilly, Johanna Mattson, Laura Jolis Lopez, Alvaro Rodriguez Lescure, Esperanza Blanco, Coralia Bueno Muino, Brian Moulton, Norma O'Donovan, Andres Hernando, Marc Nolan, Imelda Parker, Giuseppe Gullo, Bryan Hennessy. A phase III randomized study of paclitaxel (T) and trastuzumab (H) versus T, H and lapatinib (L) in first line treatment of HER2+ metastatic breast cancer (MBC) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT212.

Abstract Background Activation of the phosphoinositide -3 kinase (PI3K) pathway is a resistance mechanism to anti-HER2 targeted therapy. This trial was conducted to determine the maximum tolerated dose (MTD) of copanlisib, an oral pan-class I PI3K inhibitor, combined with trastuzumab for patients with advanced HER2 positive breast cancer resistant to anti-HER2 therapy. Patients and Methods In this phase Ib open label dose escalation study, using a 6 + 6 design, patients with advanced HER2-positive breast cancer who had disease progression following at least one prior line of HER2 therapy in the metastatic setting were treated with a dose escalation schedule of copanlisib (dose level 1 =45mg or dose level 2 = 60mg) IV on days 1, 8 and 15 of a 28 day cycle along with a fixed dose of trastuzumab 2mg/kg weekly after a loading dose of 4mg/kg in cycle 1. Archival tumour tissue, voluntary serial tumour biopsies and serial plasma samples were collected for genomic sequencing. Results Twelve patients were enrolled. MTD was determined as copanlisib 60mg plus trastuzumab 2mg/kg weekly. There was no dose limiting toxicity. The most common treatment-related adverse events (AE) of any grade experienced in more than 2 patients were hyperglycemia (58%), fatigue (58%), nausea (58%) and hypertension (50%). Confirmed stable disease at 16 weeks was observed in 6 (50%) participants. PIK3CA mutations were detected in archival tumour tissue of 6 (50%) patients and did not appear to influence likelihood of clinical benefit. PIK3CA mutations were detected in serial plasma ctDNA of all 12 patients and fluctuated over the course of treatment. Next-Generation Sequencing (NGS) analysis identified novel somatic mutations in the TTRAP gene, which encodes a PI3K-like protein kinase, detected only in tumour samples obtained at metastatic time points. Additionally, NGS analysis demonstrated clear temporal genomic heterogeneity with decreasing PIK3CA mutation variant allele frequency (VAF) post therapy Conclusions The combination of copanlisib and trastuzumab was safely administered with good overall tolerability in this trial. Preliminary anti-tumour stability was observed in patients with heavily pre-treated metastatic HER2 positive breast cancer. Translational studies identified a number of potential biomarkers for further study in the now initiated phase 2 clinical trial. Citation Format: Niamh M Keegan, Simon Furney, Janice Walshe, Giuseppe Gullo, John Kennedy, Kyran Bulger, John McCaffrey, Catherine M Kelly, Keith Egan, P O'Donovan, Andres Hernando, Ausra Teiserskiene, Imelda Parker, Angela M Farrelly, Aoife Carr, Giulio Calzaferri, Ray McDermott, Maccon M Keane, Liam Grogan, Oscar S Breathnach, Patrick G Morris, Sinead Toomey, Bryan T Hennessy. A phase Ib trial of copanlisib in combination with trastuzumab in pretreated recurrent or metastatic HER2-positive breast cancer “PantHER” [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-19-24.

Daratumumab (DARA) has shown impressive activity in combination with other agents for the treatment of multiple myeloma (MM). We conducted a phase 1b study to assess the safety and preliminary efficacy, as well as potential mechanisms of action, of DARA (16 mg/kg) in combination with a weekly schedule of subcutaneous bortezomib (1.3-1.5 mg/m2), cyclophosphamide (150-300 mg/m2), and dexamethasone (40 mg) (CyBorD DARA) as initial induction before autologous stem cell transplantation (ASCT). Eligible patients were ≤70 years of age with untreated MM requiring treatment and who lacked significant comorbidities. A total of 18 patients were enrolled. Their median age was 56 years (range, 32-66 years), and all patients had Eastern Cooperative Oncology Group performance status ≤1. The International Staging System stages were I, II, and III in 78%, 17%, and 6% of patients, respectively; 28% of patients had high-risk genetic features. There was no dose-limiting toxicity, and the incidence of grade 3 or 4 infection or neutropenia was <10%. On an intention-to-treat basis, 94% achieved ≥very good partial response with ≥complete response in 44% of patients. Among 14 of 15 patients who underwent ASCT and were evaluable for response, all 14 achieved at least very good partial response, with 8 (57%) of 14 achieving complete response. After ASCT, 10 (83%) of 12 patients in whom minimal residual disease analysis was possible were negative at a sensitivity of 10-5 (56% on intention-to-treat/whole study population) according to next-generation sequencing. Flow cytometry analysis of patient samples indicated CyBorD DARA induced activation of macrophage-mediated antibody-dependent cellular phagocytosis. This trial was registered at www.clinicaltrials.gov as #NCT02955810.

Background: Combining bevacizumab and chemotherapy produced superior response rates compared with chemotherapy alone in metastatic breast cancer. As bevacizumab may cause hypertension (HTN) and increase the risk of cardiac failure, we performed a pilot study to evaluate the feasibility and toxicity of a non-anthracycline-containing combination of docetaxel with cyclophosphamide and bevacizumab in early stage breast cancer patients. Methods: Treatment consisted of four 3-weekly cycles of docetaxel and cyclophosphamide (75/600 mg/m 2 ). Bevacizumab was administered 15 mg/kg intravenously on day 1, and then every 3 weeks to a total of 18 cycles of treatment. Serum biomarker concentrations of vascular endothelial growth factor (VEGF), cardiac troponin-I (cTnI), myeloperoxidase (MPO), and placental growth factor (PlGF) were quantified using enzyme-linked immunosorbent assay (ELISA) in 62 patients at baseline and whilst on treatment to determine their utility as biomarkers of cardiotoxicity, indicated by left ventricular ejection fraction (LVEF). Results: A total of 106 patients were accrued in nine sites. Median follow up was 65 months (1–72 months). Seventeen protocol-defined relapse events were observed, accounting for an overall disease-free survival (DFS) rate of 84%. The DFS rates for hormone receptor positive (HR+) and triple-negative (TN) patients were 95% versus 43%, respectively. The median time to relapse was 25 (12–54) months in TN patients versus 38 (22–71) months in HR+ patients. There have been 13 deaths related to breast cancer . The overall survival (OS) rate was 88%. The 5-year OS rate in HR+ versus TN was 95% versus 57%. None of the measured biomarkers predicted the development of cardiotoxicity. Conclusions: We observed a low relapse rate in node-positive, HR+ patients; however, results in TN breast cancer were less encouraging. Given the negative results of three large phase III trials, it is unlikely that this approach will be investigated further. Trial Registration ClinicalTrials.gov Identifier: NCT00911716.

Background: The phosphoinositide 3 kinase (PI3K) pathway is important in the oncogenic function of HER2. Aberrant activation of PI3K is implicated in resistance to trastuzumab and other HER2-targeted therapies and is frequent, with up to 22% of HER2 positive breast cancer having a PIK3CA mutation. Copanlisib is a pan-class 1 PI3K inhibitor administered i.v. with low nanomolar activity against both PI3Kα and PI3Kβ. Copanlisib has been shown to re-sensitise trastuzumab resistant cell lines to trastuzumab with synergism seen in some cell lines between copanlisib and HER2 targeted therapy. Trial design: This is a phase Ib open label, single arm adaptive, multi-centre trial of copanlisib in combination with T-DM1. Eligible patients will receive T-DM1 at 3.6mg/kg i.v. on day 1 of a 21-day cycle plus copanlisib. Copanlisib will be administered i.v. according to the dose escalation scheme (dose level 1 is 45mg on days 1 and 8, dose level 2 is 60mg on days 1 and 8, dose level 3 is 60mg on days 1, 8, and 15). Dose level -1 will be 45 mg on day 1 in case dose de-escalation is needed. We will enrol 3 to 6 patients per dose level. All patients in each level must have completed at least the first cycle of therapy before enrolment in the next dose level. Patients not completing the first cycle for a reason other than toxicity will be replaced. Dose escalation and determination of the Maximum Tolerated Dose (MTD) will be based on the occurrence of Dose Limiting Toxicities (DLT). Eligibility criteria: Eligible patients are those with unresectable locally advanced or metastatic HER2-positive BC who previously received trastuzumab and a taxane, separately or in combination. Participants must have adequate organ function and ECOG PS ≤ 2 Objectives: The primary objective is to determine the MTD for copanlisib in combination with T-DM1 in patients with pre-treated unresectable locally advanced or metastatic HER2-positive BC. Secondary objectives include evaluating the safety, efficacy and cardiotoxicity in patients treated with this regimen. Exploratory objectives include examining for predictive biomarkers in tumour tissue and blood or plasma and to examine molecular tumour adaptation to clinical trial therapy. Statistical methods : Patients will be accrued in cohorts of 3 patients according to a standard 3+3 algorithm, with dose escalation and determination of MTD based on the occurrence of DLT, using the usual threshold probability of 33%. The final dose level will be expanded to include a total of 6 additional patients (expansion cohort). Present accrual and target accrual: The trial will start accrual in October 2018. Maximum of 24 patients will be enrolled. Citation Format: Hassan A, Gullo G, O9Reilly S, Ruiz-Borrego M, Toomey S, Grogan L, Breathnach O, Morris PG, Walshe JM, Crown J, O9Mahony D, Falcon A, Egan K, Hernando A, Teiserskiene A, Kelly CM, Coate L, Hennessy BT. Phase Ib clinical trial of coPANlisib in combination with Trastuzumab emtansine (T-DM1) in pre-treated unresectable locally advanced or metastatic HER2-positive breAst cancer (BC) “PANTHERA”-CTRIAL-IE 17-13 [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT3-06-01.

Abstract Background The phosphoinositide 3 kinase (PI3K) pathway is important in the oncogenic function of HER2. Aberrent activation of PI3K is implicated in resistance to trastuzumab and other HER2-targeted therapies and is frequent, with up to 22% of HER2 positive breast cancer having a PIK3CA mutation. Copanlisib is a pan-class 1 PI3K inhibitor that shows particular activity against PI3Kα, the isoform encoded by the PIK3CA gene. Copanlisib has been shown to re-sensitise trastuzumab resistant cell lines to trastuzumab with synergism seen in some cell lines between copanlisib and HER2 targeted therapy. Trial design The study is a phase Ib/II open label, single arm adaptive, multi-centre trial of copanlisib in combination with trastuzumab. Eligible patients are treated with a dose escalation schedule of copanlisib IV on Days 1, 8 and 15 of a 28 day cycle with trastuzumab 2 mg/kg weekly (loading dose of 4 mg/kg in cycle 1). The phase II dose will be based on the maximum tolerated dose (MTD) established in Phase Ib. Patients are treated until radiologic or symptomatic progression, unacceptable toxicity, consent withdrawal or physician's decision. Eligibility criteria Eligible patients must have recurrent incurable or metastatic HER2-positive breast cancer that has progressed on at least one prior line of trastuzumab or T-DM1-based treatment regimen in this setting. Patients with treated and controlled brain metastases are eligible. Participants must have adequate organ function and ECOG PS ≤ 2. Patients recruited for the Phase II part of the study must have a PIK3CA mutation. Patients with uncontrolled arterial hypertension, uncontrolled diabetes or recent clinically serious infections are excluded. Specific aims The primary end point for the phase Ib part of this study is to determine the MTD for the combination. For the phase II study is anti-tumour efficacy, measured by Clinical Benefit Rate (CBR). Secondary end points are evaluation of safety and tolerability, progression-free survival, time to treatment failure, duration of response and overall survival. Incorporated translational endpoints include examination of molecular tumor adaptation in tissue and blood. Given the role of PI3K in cellular glucose metabolism, an additional exploratory objective is to determine if quantitive reduction in metabolic signal on Positron Emission Tomography-Computed Tomography (PET-CT) is predictive of benefit from therapy. Statistical methods To establish the MTD, we use a modified 3+3 design where 3 additional patients will be accrued even if the first 3 patients accrued experience no dose limiting toxicities (DLT) in sequential cohorts for a planned 12 patients. To determine the CBR, a one sample exact binomial test with a one sided significance level of 5%, 19 evaluable patients will provide >80% power to detect a difference between the null hypothesis proportion of 30% for CBR versus the alternative hypothesis proportion of 65%. Present accrual and target accrual There are 9 patients recruited so far to the phase Ib part of this study. Target accrual is 12 and for phase II is 19 patients. Contact information for people with a specific interest in the trial Prof Bryan Hennessy, Beaumont Hospital, Dublin Ireland Funded by Bayer Citation Format: Keegan NM, Walshe J, Gullo G, Kennedy J, Bulger K, Kelly CM, Crown J, Toomey S, Egan K, Kerr J, Given M, Hernando A, Teiserskiene A, Grogan L, Breathnach O, Morris PG, Keane M, Hennessy BT. A phase Ib/II trial of coPANlisib in combination with tratuzumab in pretreated recurrent or metastatic HER2-positive breast cancer “PantHER” [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT3-06-05.

Introduction: Daratumumab (DARA), a human IgG1k monoclonal antibody with single activity in multiple myeloma (MM) shows strong synergy in combination with other anti-MM agents, including immunomodulatory drug (IMiDs) and proteasome inhibitors (PI). This has led to the exploration of DARA in combination with front line regimens. Triplets including a PI and an IMiD are considered an ideal backbone with which to combine DARA prior to Autologous Stem Cell Transplantation (ASCT). However, based on the ability of Cyclophosphamide (Cy) to enhance DARA mediated antibody dependent cellular phagocytosis, we hypothesized that CyBorD may provide an alternative option (Naicker, ASH 2017). We are currently exploring the preliminary safety and efficacy of CyBorD and DARA as part of an ongoing phase 1b study in newly diagnosed MM (NDMM) pts eligible for ASCT. Last year we reported on the safety of this combination with an absence of dose limiting toxicity (DLT) with weekly subcutaneous (SQ) Bortezomib (Bor) 1.5mg/m2, Cy 300mg/m2 and DARA 16mg/kg (McEllistrim, ASH 2017). We now report on the efficacy of this regimen as pre-transplant induction, including the rate of CR post ASCT.

1036 Background: PI3K pathway activation is implicated in resistance to trastuzumab (T) therapy in breast cancer (BC). Copanlisib (C) is a pan-class I PI3K inhibitor with particular activity against PI3Kα, the isoform encoded by the PIK3CA gene. PIK3CA mutation may predict response to PI3K inhibition. Methods: The maximum tolerated dose (MTD) and safety of C + T were evaluated in an open label, single arm, adaptive multicenter phase Ib dose escalation clinical trial in patients (pts) with HER-2 positive BC. Eligible pts had disease progression following at least one line of (T) or TDM-1 based therapy in the metastatic setting. Pts were treated with T (4mg/kg loading dose then 2mg/kg weekly) given with C intravenously on Day 1, 8 + 15 of 28 day cycle at one of two dose levels (DL) according to a modified 3+3 (6+6) design. Cycle 1 safety data were used to determine dose limiting toxicities (DLTs). Disease assessments were made every 8 weeks. PIK3CA mutation status was determined in formalin-fixed paraffin-embedded (FFPE) primary tumor blocks by standard sequencing and in serial samples of plasma circulating tumor DNA (ctDNA) during treatment by droplet digital PCR. Results: Twelve pts were treated with C + T, 6 on DL1 (45mg) and 6 on DL2 (60mg). Median age was 53yrs. Pts had 15 to 85 months of prior therapy in the metastatic setting with a median of 4 prior lines. There were no DLTs. The MTD and recommended dose for phase II is 60mg. Eleven SAEs were reported. Of these, 36% (n = 4) were infections requiring hospitalization and all resolved with no changes in dose. Grade(G) 3 lung infection and G3 abdominal pain SAEs were reported possibly related to C. All others were considered unlikely or not related to C. G3 liver enzyme rise was reported in 1 pt with a single episode of G4 rise in GGT. G3 hypertension was reported in 33% (n = 4) pts. Best response was stable disease in 9/12 pts and 6 pts continued treatment ≥16 weeks. PIK3CA mutation was positive in 6/12 (50%) of tumors. Concordance between PIK3CA mutation in tissue and plasma pre-treatment was 80% with evidence of dynamic change in quantity of mutation during treatment. Conclusions: C+T is a safe, well tolerated combination. Efficacy of C+T will be assessed in a phase 2 study at the MTD of 60mg. Clinical trial information: NCT02705859.

Background: PIK3CA is mutated in up to 20% of HER2 positive breast cancers, contributes to HER-2 therapy resistance and may be predictive of response to PI3K inhibitor therapy. PIK3CA mutations in breast cancer occur primarily at hotspots E545K at exon 9 and H1047R at exon 20. Copanlisib (C) is a pan-class I PI3K inhibitor that shows particular activity against PI3Kα, the isoform encoded by the PIK3CA gene. The aim of this study was to assess PIK3CA mutation status in matched tumour and plasma samples pre copanlisib treatment and to monitor PIK3CA mutation concentration changes in plasma over the course of PI3K inhibition therapy. Methods: For 12 patients with advanced HER2 positive, breast cancer treated on a clinical trial of copanlisib and trastuzumab, we prospectively examined serial plasma samples to quantify the PIK3CA hotspot mutations in circulating tumour DNA by droplet digital PCR (ddPCR). Samples were taken pre-treatment, then every two weeks on treatment and immediately after radiological disease progression. Archival formalin fixed paraffin embedded (FFPE) primary tumour tissue were examined using MassArray® to detect PIK3CA mutation. Results: PIK3CA mutations were detected in 6/12 (50%) archival FFPE primary tumours ; either an exon 9 (n = 2) or exon 20 (n = 4), all of which were also oestrogen receptor positive and had at least one prior line of anti Her2 therapy in the advanced cancer setting. There were 106 plasma samples included in the mutation analysis. PIK3CA mutation (H1047R or E545K) >500copies/mL were detected in 66% (70/106) of the samples. Of the six tumour samples that had no PIK3CA mutation detected, three had >500copies/mL (range: 0-25,500copies/mL) of mutated PIK3CA detected in serial plasma samples. Variations in plasma DNA mutation levels over time were found in all 12 patients. Conclusions: Our data demonstrate that PIK3CA mutation is detectable in the plasma of a large proportion of a cohort of patients with HER2 therapy resistant advanced breast cancer, is potentially a more meaningful representation of current mutation status than archival primary tumour tissue given discordance and levels of mutation fluctuate with PI3K inhibition combined with trastuzumab. Legal entity responsible for the study: Cancer Trials Ireland. Funding: Bayer Pharmaceuticals. Disclosure: B. Hennessy: Research funding: Bayer Pharmaceuticals. All other authors have declared no conflicts of interest.

Introduction: Daratumumab (DARA) is a human IgG1k monoclonal antibody licenced for second line use as monotherapy or in combination with either lenalidomide or bortezomib (Bor) plus dexamethasone (D) for patients (pts) who have received at least one prior therapy. There are no published data on front line use of DARA in combination regimens. CyBorD is considered a safe and effective induction regimen for patients with newly diagnosed MM eligible for transplantation. Up to 60% of patients achieve very good partial response (VGPR) or better following 4 cycles of induction (Reeder CB et al, Blood 2010). Since our pre-clinical data showed enhanced antibody dependent cellular phagocytosis (ADCP) following Cyclophosphamide (Cy) exposure (Rigalou et al, ASH 2016), we set out to explore the feasibility of combining DARA with weekly CyBorD in newly diagnosed transplant eligible MM patients. We aim to demonstrate safety, efficacy, convenience and cost-effectiveness in a Phase 1b clinical trial of newly diagnosed patients with MM. Methods: This ongoing phase Ib, open-label, single arm, dose escalation study has recruited 12 patients from November 2016 to June 2017 across 3 sites in Ireland (3 pts in DL 1, 3 pts in DL 2 and 6 pts in DL 3). Baseline demographic factors include: 75% males, 25% females; median age of 57.5 years (35-66 years); 83% ISS stage I, 17% ISS stage II/III. FISH analysis detected t(4;14) in 0% of pts (0/12), t(14;16) in 0% of pts (0/12) and del17p in 17% of pts (2/12). The study is designed to assess the safety and efficacy of 4 cycles of induction therapy with Cy and Bor on days 1, 8, 15 and 22, D 20/mg/day on days 1, 2, 8, 9, 15, 16, 22 and 23 and DARA 16mg/kg on days 1, 8, 15 and 22 for cycles 1 and 2 and on days 1 and 15 for cycles 3 and 4. Following the induction therapy, patients proceed with stem cell mobilization and high dose Melphalan 200mg/m2 autologous stem cell transplant (ASCT). Following SCT 2 cycles of consolidation therapy with Cy and Bor on days 1, 8, 15 and 22, D 20/mg/day on days 1, 2, 8, 9, 15, 16, 22 and 23 and DARA 16mg/kg on days 1 and 15 were administered. After consolidation therapy, all patients are scheduled to receive DARA maintenance on day 1 every 4 weeks until progression, unacceptable toxicity or withdrawal of consent (limited to a maximum duration of 2 years). Patients with high-risk features receive subcutaneous (SQ) Bor on days 1 and 15 during maintenance phase. We used a standard 3+3 design in sequential cohorts (3 dose levels (DL) of Cy and Bor: DL 1: Cy 150mg/m2 and Bor 1.3mg/m2, DL 2: Cy 300mg/m2 and Bor 1.3mg/m2 and DL 3: Cy 300mg/m2 and Bor 1.5mg/m2; and a DL -1: Cy 100mg/m2 and Bor 1.3mg/m2. Six additional patients will be enrolled in an expansion cohort as the maximum tolerated dose (MTD) has been determined as DL 3. The primary endpoints are the incidence of dose limiting toxicity (DLT) within the first cycle of combination at each dose level and complete response (CR) rate post ASCT. Secondary endpoints include: safety, CR rates at the end of induction, consolidation and maintenance, best overall response, minimal residual disease (MRD) negative rate, progression-free survival, clinical benefit rate and overall survival. Response will be investigator-assessed as per IMWG criteria. This trial is registered at www.clinicaltrials.gov as NCT02955810. Results: We report the safety data from interim analysis following completion of the dose escalation phase of CyBorD-DARA trial. The most common adverse events (AE) of grade 3 severity or higher were thrombocytopenia, postoperative wound infection, urinary tract infection, hyponatraemia, back pain, bone pain. Five serious adverse events (SAE) were reported but none related to the study treatment. No DLT occurred in any group. To date all pts continue on treatment and enrolment is ongoing. Although follow up is still short, the combination shows a promising response rate. Following 4 cycles of induction therapy the first 6 patients enrolled (at DL1 and DL2) have achieved VGPR or better. Safety and efficacy data will be updated at ASH meeting. Conclusion: DARA can be safely combined with weekly CyBorD. MTD/RP2D is Cy 300mg/m2 and Bor 1.5mg/m2 in combination with D and DARA and early analysis demonstrates promising efficacy. Disclosures O'Dwyer: Onkimmune Ltd: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; GlycoMimetics Inc: Research Funding.

Abstract Background: LDE225 is a potent and selective oral inhibitor of Smo, a key component of the hedgehog (Hh) signaling pathway. Up-regulation of the Hh pathway is implicated in the genesis of a wide range of tumors including triple negative breast cancer. Here we report an ongoing phase I study exploring the combination of LDE225 with docetaxel in TN ABC patients to identify the Maximum Tolerated Dose (MTD) and the Recommended Phase II Dose (RP2D) (ClinicalTrials.gov Identifier: NCT02027376). Trial Design: Eligibility criteria include patients with TN ABC candidates to receive treatment with docetaxel that have received a maximum of 3 prior chemotherapy regimens. Those patients with CNS involvement are also candidates if treated and clinically stable. Treatment consists of 21-day cycles with docetaxel 75mg/m2 on day 1, every 21 day and LDE225 once daily. We use a standard 3+3 design in sequential cohorts (3 dose levels (DL) of LDE225: 400mg once daily (DL1), 600mg once daily (DL2), 800mg once daily (DL3); and a DL-1: LDE225 400mg once daily and docetaxel 60mg/m2 every three weeks). The primary endpoint is the MTD and RP2D of the combination; secondary endpoints include evaluation of safety and tolerability, in addition to pharmacodynamic (PD) and pharmacokinetic (PK) studies. Patients are treated until radiologic or symptomatic progression or unacceptable toxicity occurs. PK will be performed to evaluate whether LDE225 influences the pharmacology of docetaxel. PD assessments include Hg gene expression signature associated to pathway activation in tumor samples and changes in Smo related biomarkers in skin and blood correlative samples. Efficacy will be measured in terms of time to progression and objective response rate. A minimum of 9 and a maximum of 18 patients will be included in this phase I. The study is approved by ERBs and Competent Authority and already recruiting patients (two patients included in DL1). Citation Format: Miguel Martin, Manuel Ruiz-Borrego, José M Trigo, Silvia Antolin, Jose A Garcia-Saenz, Andres Hernando, Alberto Ocaña, Federico Rojo, Sara Lopez-Tarruella, Jesus Corral, Nuria Ribelles, Lourdes Calvo, Fernando Moreno, Rosalia Caballero, Eva Carrasco. A phase I study of LDE225 in combination with docetaxel in patients with triple negative (TN) advanced breast cancer (ABC): GEICAM/2012-12 (EDALINE study) [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr OT1-1-06.

Background: LDE225 is a potent and selective oral inhibitor of Smo, a key component of the hedgehog (Hh) signaling pathway. Up-regulation of the Hh pathway is implicated in the genesis of a wide range of tumors including triple negative breast cancer. Here we report an ongoing phase I study exploring the combination of LDE225 with docetaxel in TN ABC patients to identify the Maximum Tolerated Dose (MTD) and the Recommended Phase II Dose (RP2D) (ClinicalTrials.gov Identifier: NCT02027376).