BACKGROUND:Bone metastases (BM) from breast cancer cause significant cancer-induced bone pain (CIBP). Management of CIBP is primarily with opioids, which have notable side effects. In preclinical models, cannabinoid receptor (CB)2 and CB1 agonists were shown to decrease CIBP and bone degradation. We hypothesized that the addition of CB2/CB1 agonists would decrease opioid requirements in patients with BM. METHODS:We conducted a single-arm study among breast cancer patients with BM on opioid therapy. Patients were treated with 10 mg dronabinol BID for 8 weeks. Our primary objective was to determine the proportion who decreased their opioid use by ≥ 20%. Participants completed the Brief Pain Inventory and the European Organization for Research and Treatment of Cancer quality of life questionnaires before and after treatment. Pre- and post-treatment blood and urine were collected for analysis of biomarkers of bone remodeling. RESULTS:We enrolled 14 evaluable patients, and 4 decreased opioid use by ≥ 20%, meeting the primary endpoint. Patients reported significant improvements in pain severity, interference scores, quality of life, and insomnia. There was one grade 3 adverse event (dizziness) related to the study drug. A significant decrease was noted in serum C-terminal telopeptide levels with therapy. CONCLUSION:Our pilot study shows that the addition of dronabinol resulted in decreased opioid requirements for CIBP. Patient-reported outcomes also demonstrated improved pain and QOL with addition of dronabinol. Our results are promising and warrant further investigation into novel analgesics for CIBP to decrease opioid use.ClinicalTrials.gov NCT03661892.

Due to limited certified genetic counselor resources as well as increasing referral volumes, long wait times for genetics appointments were negatively impacting timely patient care at our institution in 2018. Using existing staff resources, we designed and implemented a collaborative workflow that integrated pretest genetic counseling and consent by our breast clinic physician assistant during either initial high-risk clinic appointment or as part of the new breast cancer diagnosis work-up. After 6 months of using the new model, wait times for pretest genetic counseling for new patients with breast cancer decreased from 116 to 13 business days, and we saw an increase in genetic counseling volumes of nearly 30%. There were no errors or discrepancies in test selection or testing criteria in the 62 patients seen by the physician assistant for pretest counseling. Barriers to the new workflow included a low completion rate of a preappointment survey used to generate the patient pedigree, which required significant effort at the appointment to manually gather this information. Although this workflow was highly successful at the time, it was ultimately discontinued due to internal staffing changes and updates to national guidelines for genetic testing. However, implementing this model illustrates a practical, low-cost way to manage genetic testing referrals in a timely fashion and increase volumes of appropriate testing in a setting with limited certified genetic counselor resources and was highly effective in our institution for several years.

INTRODUCTION:Chemotherapy-induced alopecia (CIA) is known to have a significant psychological and quality of life impact. Although cold caps have been shown to prevent CIA, expense and extension of treatment durations are barriers for routine clinical use. Keratinocyte growth factor (KGF) has been shown to have cytoprotective effects on human hair follicles and reduce alopecia in preclinical models. We hypothesized that KGF-hair serum (KGF-HS) will prevent CIA. METHODS:We conducted a Simon two-stage, single-arm clinical study in women with early-stage breast cancer (ESBC) scheduled to receive at least four cycles of chemotherapy. The primary outcome was preservation of hair after chemotherapy, whereas secondary measures included patient-reported wig use, comfort, and validated quality-of-life instruments (EORTC QLQ-C30, HADS, and BIS). RESULTS:Twenty patients were evaluable for the primary end point. None achieved meaningful hair preservation. The average duration of treatment of KGF-HS application was 4.6 weeks. CONCLUSION:In this study of women with ESBC receiving chemotherapy, using the KGF-HS did not prevent CIA. There was no statistical difference pre- and post-study BIS, HADS, and EORTC-30 scores. Application of the KGF-HS was reported to be easy, with minimal discomfort, and a non-oily appearance. Patients' ease of use and acceptability of a topical agent for CIA further supports the development of new agents for a more practical and affordable alternative to scalp cooling. TRIAL REGISTRATION:clinicaltrials.gov: NCT04554732.

e13109 Background: There is a significant unmet need among patients with PD-L1 low/negative metastatic triple-negative breast cancer (mTNBC). >95% of TNBCs are positive for C-C chemokine receptor 5 (CCR5). Leronlimab (LRM) is a humanized monoclonal antibody given subcutaneously which blocks CCR5 and in a preclinical model reduced TNBC metastasis by more than 98%. Methods: In this post hoc analysis LRM safety and efficacy data were pooled from 28 mTNBC patients from 3 clinical trials (NCT03838367; NCT04313075; NCT04504942). LRM was given weekly at a dose of 350 mg (N=10), 525 mg (N=15), or 700 mg (N=3) in combination with various chemotherapies ± immune checkpoint inhibitors (ICI). PD-L1 staining (LifetracDx) was measured on cancer-associated macrophage-like cells (CAMLs) and circulating tumor cells (CTCs) prior to and after (≈40 days) LRM treatment. Results: Median age was 48.5 years (range 32-83) with a median of 2 prior metastatic therapies (range 0 to 5). Ten patients (35.7%) had non-visceral metastases; 18 (64.3%) had visceral metastases, including 7 (25.0%) with brain metastases. The most common treatment-emergent adverse events (TEAEs), at a rate of ≥10%, were fatigue (21.4%), headache (21.4%), anemia (10.7%), constipation (10.7%), nausea (10.7%), and decreased neutrophil count (10.7%) but with no febrile neutropenia events. Overall, 21.4% (6/28) patients reported any LRM treatment-related TEAE; of these none were classified as CTCAE grade >2. No patients discontinued treatment due to a LRM treatment-related TEAE. Overall, 35.7% (10/28) reported any serious TEAE; none of the serious TEAEs were considered related to LRM treatment. The median overall survival (OS) was 7.1 months. Survival at 1, 2, 3, 4, and 5 years was 35.7%, 21.4%, 17.9%, and 17.9%, 17.9%, respectively. OS among the 7 patients treated with LRM with an ICI, or followed by an ICI, was longer than among the remaining 21 patients (HR 4.14, 95% CI: 1.7–10.2; P=0.0041). For patients with available data, upregulation from baseline of PD-L1 was observed on CAMLs/CTCs in 76% (16/21) of patients. All five patients treated with LRM [525 mg (N=4), or 700 mg (N=1)] with an ICI, or followed by an ICI, and who significantly upregulated PD-L1, remained alive at 5 years. Conclusions: In this post hoc analysis LRM was well tolerated with no LRM treatment-related TEAEs leading to treatment discontinuation and no LRM treatment-related TEAEs graded as CTCAE >2. A 5-year OS rate of 17.9% (5/28) in this advanced population is encouraging. All 5 patients with PD-L1 upregulation treated with LRM with an ICI, or followed by an ICI, remained alive at 5 years suggesting a correlation with durable responses. These findings support the hypothesis that LRM may enhance PD-L1 expression on CAMLs/CTCs, potentially priming tumors for improved responses to ICIs. Confirmatory phase 2 studies in mTNBC are planned. Clinical trial information: NCT03838367 (N=10); NCT04313075 (N=16); and NCT04504942 (N=2).

TPS655 Background: Early (14-28 day) on-treatment suppression of tumor proliferation during neoadjuvant endocrine therapy (NET) is strongly associated with favorable long-term outcomes in estrogen receptor–positive (ER+) HER2– breast cancer. In premenopausal women, tamoxifen with or without ovarian function suppression (OFS) results in suboptimal Ki-67 suppression compared with aromatase inhibitor + OFS. (Z)-endoxifen (ENDX), the active metabolite of tamoxifen, dually inhibits ER signaling and PKCβ1-mediated AKT activation, supporting its evaluation as an alternative NET strategy in this population. Methods: EVANGELINE (NCT05607004) is an ongoing, multicenter, open-label Phase 2 study evaluating daily 40 mg ENDX plus goserelin administered every 28 days as neoadjuvant therapy in premenopausal women with ER+/HER2–, cT2–3, cN0–1 breast cancer. The primary objective is to determine the proportion of patients with baseline Ki-67 >10% who achieve Ki-67 ≤10% after 4 weeks of therapy. A Simon two-stage design is used to test whether the Week 4 Ki-67 ≤10% rate is at least 65%, with 20 patients enrolled into the first stage and, if promising, another 25 patients enrolled into the second stage (cohort A). A parallel cohort of 20 patients with baseline Ki-67 ≤10% (cohort B) is enrolled to assess objective response rate (ORR) at 24 weeks per RECIST v1.1. Secondary objectives include examining safety and tolerability, residual cancer burden, and PEPI score. Correlative analyses include examining effect of treatment on select tumor and plasma biomarkers. Clinical trial information: NCT05607004 .

1077 Background: Endocrine therapy (ET) resistance is common in estrogen receptor-positive (ER+) metastatic breast cancer (BC), where bone metastases (BMET) are usually the first sign of spread. ER signaling and ET effects can depend on other steroid hormones receptors (SHRs), such as progesterone receptors (PR) and androgen receptors (AR). However, the roles of these receptors in ER+ BC BMET are underexplored. To address this gap, PR and AR protein expression in HER2-/ER+ BMET and associations with overall survival (OS) were examined. Methods: In a retrospective analysis on BC BMET samples analyzed at Caris Life Sciences, n = 2038 HER2- BMETS were identified by immunohistochemistry (IHC) (≤1+intensity or ≤10% staining, or 2+ & > 10% with CISH-null reflex test). HER2- ER+ (by IHC, ≥1+ & ≥1%) BMETs (“ER+ BMET” n = 1700; 84.5% of total) were then examined for prevalence of IHC+ SHR expression (PR: ≥1+ & ≥1%; AR: ≥1+ & ≥10%) and associated pathogenic/likely pathogenic ESR1 or PIK3CA gene mutations (mut). Associations of SHR status with clinical outcomes were tested by inferring OS from biopsy collection or start of therapy to last contact. Results: Most ER+ BMET expressed PR (59.3%) or AR (87.1%). Only 9.4% of PR+/ER+ BMET were AR-null, while 38.2% of AR+/ER+ BMET were PR-null. Overall, “triple positive” (AR+/PR+/ER+) BMET comprised the largest group (53.7%), followed by PR-null AR+/ER+ BMET (33.2%). AR-null ER+ BMET with (5.6%) or without PR (7.3%) were less common. AR+ status was associated with better outcomes for ER+ BMET patients (pts) with longest OS for “triple positive”, while “loss” of PR was associated with shorter OS (Cox proportional hazards ratio (HR) = 1.37, p < 0.0001). AR-null status was associated with worse OS compared to “triple positive” regardless of PR status (AR-/PR- HR = 1.66, p < 0.001; AR-/PR+ HR = 1.85, p < 0.0001). In ER+ BMET with ESR1mut (16.3%), OS for triple positive tumors, which were more prevalent (74.0%) due to increased PR expression, was reduced (HR = 1.92, p < 0.0001 vs ESR1wt ). For PIK3CA , “loss” of PR abrogates benefits associated with AR+ status only in PIK3CAmut pts (48.7%) with patterns between SHR groups otherwise maintained. Among ER+ BMET pts who received aromatase inhibitors or fulvestrant, AR+ status was associated with the best OS, regardless of PR status, where treatment was associated with significantly longer OS (vs no treatment) across SHR groups, except in PR+/AR-null. For ER+ BMET pts treated with CDK4/6 inhibitors, OS was highest in the “triple positive” cohort, with onlyAR+ SHR groups demonstrating improved OS with treatment. Conclusions: Based on this analysis, AR expression is more prognostic of OS than PR, regardless of treatment, in pts with ER+ BC BMETs, with “triple positive” BMETs generally associated with the best OS. Research on SHRs as mediators vs biomarkers of risk in ER+ BC BMETs is needed to provide direction for possible therapeutic targeting.

While the importance of estrogen in driving ER+ breast cancer progression is clear, data from pre-clinical studies exploring the role of tumoral progesterone (PR) and androgen (AR) receptors are conflicting, likely due in part to the promiscuity of steroid receptor ligands, as well as relative levels of steroid hormone receptor expression and of steroid hormones within the tumor milieu. While bone is usually the first site of metastases in ER+ metastatic breast cancer, the roles of tumoral PR and AR (present in 58 percent and 86 percent of clinical ER+ bone metastases [BMET], respectively) in ER+ breast cancer progression at this site have not been well studied. Studies were undertaken to examine the effects of ovariectomy (OVX), a model of surgical menopause that significantly reduces endogenous progesterone and androgen levels, in a pre-clinical model of human ER+ bone metastases that is dependent on exogenous 17ß-estradiol (E2) supplementation. Effects of OVX (at 9-weeks of age) were ascertained using skeletally mature female nude mice supplemented with a modest dose of E2 (0.36 mg 60 day pellets) prior to intracardiac inoculation (at 10 weeks of age) with bone metastasis-derived MCF7 cells (43.4M cells) that form robust E2- and TGFß-dependent osteolytic metastasis in vivo, and express PR and AR in vitro. Osteolytic bone metastatic lesions in E2-supplemented mice were reduced in both incidence and size in OVX (vs ovary intact) mice. Anti-tumoral effects of OVX were not limited to bone; E2-driven orthotopic tumor progression was similarly reduced. Histologic assessment of cytokeratin-positive breast cancer tumor cells within bone revealed a small but statistically significant reduction in Ki67-positivity in OVX (vs ovary -intact) mice that correlated with osteolytic lesion size. In addition, PR and AR expression in BMET lesions, which was readily detected by IHC in ovary-intact mice, was markedly reduced in OVX mice. While additional experiments are underway to query possible roles of specific reproductive hormones altered in OVX mice, these results are consistent with the postulate that tumoral AR and PR signaling may promote ER+ bone metastases progression in this model. In addition, while ovariectomy is a common pre-clinical means of reducing estrogen to model natural menopause in women, resultant changes in steroid receptor signaling are clearly much more complex. Funding: NIH 5R25CA275753, 5P30CA023074 Date of Presentation October 17, 2024

1010 Background: ctDNA monitoring during adjuvant endocrine therapy is an opportunity to detect molecular relapse before clinically apparent recurrence. ctDNA positivity rates, dynamics and the frequency of asymptomatic imaging-detectable metastatic disease at the time of ctDNA detection remain unknown in high-risk ER+/HER2- BCs. We present ctDNA results from a prospective, multicenter, randomized ctDNA interventional trial, DARE (NCT04567420). Methods: Patients receiving adjuvant endocrine therapy for >6 months but <7 years, with either recurrence risk >15% (PREDICT, RSPC, CTS5), >4 positive axillary lymph nodes, (primary tumor >5 cm, or 1-3 positive nodes with grade 3 histology, or >3 cm tumor, or high molecular risk (Oncotype Dx RS >26, MammaPrint high risk, EndoPredict >4, Prosigna score >60) were eligible for ctDNA surveillance with the Signatera assay (Natera, Inc.) every 6 months. ctDNA+ patients had systemic staging with imaging and if there was no evidence of metastatic disease patients were randomized to switching to fulvestrant + palbociclib (Arm A) or to continuation of adjuvant therapy (Arm B). Negative predictive value (NPV) was calculated for recurrence in the screening group after each ctDNA- test. In randomized patients, early ctDNA dynamics were correlated with recurrence-free survival (RFS) and ctDNA clearance rates were calculated by trial arm. Results: 552 patients had tissue sent for assay design; 494 had ctDNA results; 52 failed WES and/or had incomplete tumor/normal/blood sets; 6 had pending reports. Among patients not randomized, 432 were ctDNA-, of these N=43 had one time point and 389 had >2 ctDNA- result, overall median screening time 27.4 months (0-45.5), 4 ctDNA- patients had recurrence (NPV 100% at 6 months and 99% at 12 months post-testing). Forty patients were randomized, 34 had post-randomization ctDNA result. Randomization rates were 53% and 76% for patients who tested ctDNA-positive on the first screening (N=19) versus those who turned positive in follow up testing (N=15). At any time post-randomization, ctDNA clearance rates were 63% (10/16) in Arm A and 22% (4/18) in Arm B. Among randomized patients, 6 of 9 patients with increased ctDNA levels from the pre-randomization to the 3-month on-treatment recurred (median time to recurrence 4.8 months, range: 3.3-24.3), among those with a decrease in ctDNA post-treatment only 1 of 6 experienced recurrence at 10.3 months (HR: 5.3, 95% CI: 1.1-53, p=0.04). Conclusions: This study demonstrates the ability of ctDNA to identify breast cancer patients at high risk of relapse for randomization in a prospective, multicenter, randomized clinical trial. Patients with serially ctDNA- results during surveillance had 99% RFS after a median f/u of 27.4 months. Interim analysis revealed higher clearance rates in Arm A compared to patients randomized to Arm B. Early on treatment ctDNA dynamics is prognostic of patient outcomes. Clinical trial information: NCT04567420 .

Abstract Background: ctDNA monitoring during adjuvant endocrine therapy provides an opportunity to detect molecular relapse before clinically apparent recurrence. The rate and dynamics of ctDNA positivity and the frequency of asymptomatic but imaging detectable metastatic disease at the time of ctDNA detection remain unknown in high-risk ER+/HER2- breast cancers. We present results of ctDNA positivity rates in 508 and imaging results in ctDNA+ patients from a prospective, multicenter, randomized ctDNA surveillance and intervention trial, DARE (NCT04567420). Patients and methods: Patients receiving adjuvant endocrine therapy for > 6 months but < 7 years, with either (i) risk of recurrence > 15% calculated by PREDICT, RSPC, or CTS5, or (ii) > 4 positive axillary lymph nodes, or (iii) primary tumor > 5 cm, or (iv) 1-3 positive nodes with grade 3 histology, or > 3 cm tumor, or Oncotype Dx RS > 26, MammaPrint high risk, EndoPredict > 4, Prosigna score > 60 were eligible for ctDNA surveillance with the SignateraTM assay (Natera Inc.) every 4-6 months during routine follow up visits. ctDNA+ patients underwent systemic staging with imaging and randomized to continuation of adjuvant therapy versus switching to fulvestrant plus palbociclib if there was no evidence of distant metastatic disease. The primary objectives are to assess the incidence of ctDNA positivity in the surveillance phase and to assess if palbociclib plus fulvestrant improves relapse-free survival in 100 randomized patients. This is an updated, protocol-driven interim report to determine if screening eligibility criteria needs to be revised to keep randomization rate > 15% of the screened population. Results: The trial is open at 15 sites and enrolled 508 patients between May 2021 and June 2023; 882 plasma ctDNA tests were performed successfully in 364 patients (72%). The most common reason for failure to generate a personalized ctDNA assay was insufficient tissue submitted, 78% of failed tests were due to preanalytical failure, the technical failure rate was 22%. Thirty patients, 8.2% of those with results available, had >1 positive ctDNA result, the overall positivity rate across all assays was 3.4% (n=30/882). Patient characteristics are shown in the table (not all patients have complete data), 47% of ctDNA+ cases had >4 + lymph nodes. ctDNA positivity rate in the first test was 3.8%, and anytime ctDNA detection rate among those with serial testing was 7.2%. Among ctDNA+ patients, the first ctDNA draw was positive in 23 of 30 cases (77%) with 36.5 months median time (range 6-102 months) from surgery to testing. Using 12 months interval brackets from surgery to 1st ctDNA positivity, annual detection rates were 2,3% (1/44), 8.5% (7/82), 10.8% (9/83), 7.5% (4/53), 13,2% (5/38), and 6.2% (4/64), at 1st, 2nd, 3rd, 4th and > 5th year post-surgery, respectively, due to small sample sizes, 95% confidence broadly overlap. Five ctDNA+ patients (16.7%) had asymptomatic, imaging-detectable metastatic disease, 22 ctDNA+ patients were randomized, the goal is to accrue a total of 100 patients. Conclusions: ctDNA surveillance of ER+/HER2- breast cancers during adjuvant endocrine therapy indicate 8.3% detection rate at patient level and 3.4% at assay level. Serial screening increases detection rates as 23% of positive ctDNA tests occurred after an initial negative result. 83% of ctDNA+ patients had true molecular relapse without imaging detectable metastatic disease. Eligibility for screening on the trial is now restricted to patients with >4 + lymph nodes, randomization is open for any patients who are ctDNA+ including routine commercial screening. Table of patient characteristics with ctDNA result (n=364) ctDNA+ (n=30) Age < 50 29% 23% Age >50 71% 77% PR + 78% 73% PR - 7% 17% HER2 IHC negative 79% 77% Grade 1 8% 7% Grade 2 53% 50% Grade 3 29% 37% T 1 19% 17% T2 43% 43% T3 27% 27% T4 2% 7% 0 +nodes 12% 12% 1 +node 24% 10% 2 +nodes 15% 13% 3 +nodes 8% 13% >4 +nodes 0 47% Citation Format: Lajos Pusztai, Ekaterina Kalashnikova, Evthokia Hobbs, Ursa Brown-Glaberman, Monica Mita, Paula Klein, Fengting Yan, Sima Ehsani, Wajeeha Razaq, Alison Stopeck, Manali Bhave, Michelle Loch, Sagar Sardesai, Evanthia Roussos Torres, Mark Burkard, Femi Okubanjo, Eric Gauthier, Angel Rodriguez, Minetta Liu, Peter Kabos. Circulating tumor DNA (ctDNA) monitoring of estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) high risk breast cancer during adjuvant endocrine therapy [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 PS06-02.

Breast cancer bone metastases (BMET) are incurable, primarily osteolytic, and occur most commonly in estrogen receptor-α positive (ER+) breast cancer. ER+ human breast cancer BMET modeling in mice has demonstrated an estrogen (E2)-dependent increase in tumor-associated osteolysis and bone-resorbing osteoclasts, independent of estrogenic effects on tumor proliferation or bone turnover, suggesting a possible mechanistic link between tumoral ERα-driven osteolysis and ER+ bone progression. To explore this question, inducible secretion of the osteolytic factor, parathyroid hormone-related protein (PTHrP), was utilized as an in vitro screening bioassay to query the osteolytic potential of estrogen receptor- and signaling pathway-specific ligands in BMET-forming ER+ human breast cancer cells expressing ERα, ERß, and G protein-coupled ER. After identifying genomic ERα signaling, also responsibility for estrogen's proliferative effects, as necessary and sufficient for osteolytic PTHrP secretion, in vivo effects of a genomic-only ER agonist, estetrol (E4), on osteolytic ER+ BMET progression were examined. Surprisingly, while pharmacologic effects of E4 on estrogen-dependent tissues, including bone, were evident, E4 did not support osteolytic BMET progression (vs robust E2 effects), suggesting an important role for nongenomic ER signaling in ER+ metastatic progression at this site. Because bone effects of E4 did not completely recapitulate those of E2, the relative importance of nongenomic ER signaling in tumor vs bone cannot be ascertained here. Nonetheless, these intriguing findings suggest that targeted manipulation of estrogen signaling to mitigate ER+ metastatic progression in bone may require a nuanced approach, considering genomic and nongenomic effects of ER signaling on both sides of the tumor/bone interface.

1018 Background: Brain metastases (BM) in breast cancer (BC) have a poor prognosis, with median survival at 7.2-13 months. Interplay between genomic evolution of cancer cells and development of BM is obscure. We sought to identify genomic aberrations associated with BM. Methods: We included 14095 BC samples: 429 BM, 7858 extra-cerebral metastases (ECM) and 5808 primary tumors (PT) were analyzed by next generation sequencing of DNA (NextSeq, 592 genes and NovaSeq, WES) and RNA (NovaSeq, WTS) (Caris Life Sciences, AZ). Tumor mutational burden-high (TMB-H) was defined as ≥10 mt/MB. Cut-off for PD-L1 immunohistochemistry positivity was ≥2 intensity and >5% staining (SP142). Global loss of heterozygosity (gLOH) used a cut-off of ≥ 16%. PAM50 was evaluable for a subset (n=9724, 69%) with WTS data. Statistical significance determined using chi-square and Mann-Whitney U test and adjusted for multiple comparisons (q<0.05). Results: Median age was lower in BM than ECM and PT (55 vs 62 vs 59 years, q<0.05). BM subtype was triple negative (TNBC, 40.1%), HR+/HER2- (30.5%), or HER2+ (29.4%) vs. ECM primarily HR+/HER2- (65.4%) and PT HER2+ (52.5%). BM were Basal-like (35.3%) or HER2-enriched (35.3%), whereas ECM were Luminal B (47.2%) and PT were Basal-like (34.4%) or Luminal B (34.6%). The Table summarizes molecular findings. In HR+/HER2- BC, BM were associated with TMB-H vs. ECM and PT (q<0.05). BM had higher GATA3-mt and ESR1-mt compared to PT (q<0.05). In HER2+ BC, BM had lower PD-L1+ (11.8% vs 39.3%) and higher ESR1-mt than PT. BM had higher ERBB2-amp (93.5% vs 75.2%) and RARA-amp (27.3% vs 6.7%) than PT (q<0.05). TNBC BM had higher proportion of TMB-H tumors but lower PD-L1+ (20.8% vs 50.7%) than PT. BM had increased gLOH than ECM (59.2% vs 36.2%). PIK3CA was lower in BM vs. ECM. In all subtypes, BM, when compared to ECM and PT respectively, were associated with decreased AR+ (HR+/HER2-: 57.7% vs 80.8% vs 85.7%; HER2+: 54.4% vs 77.1% vs 81%; TNBC: 15.1% vs 27.7% vs 23.1%), increased dendritic cell infiltration (HR+/HER2-: 3.2% vs 2.6% vs 2.5%; HER2+: 3.85% vs 2.41% vs 2.36%; TNBC: 3.96% vs 2.89% vs 3.05%) but lower IFN score (HR+/HER2-: -0.56 vs -0.41 vs-0.35; HER2+: -0.53 vs -0.39 vs -0.30; TNBC: -0.55 vs -0.30 vs -0.28). Conclusions: BM in BC are more frequently associated with TNBC and Basal-like BC phenotypes than ECM or PTs. BM have a higher proportion of ESR1-mut than PTs, highlighting a possible association between endocrine resistance and development of BM. BM had lower IFN score and PDL-1 expression highlighting an immunosuppressed tumor microenvironment. [Table: see text]

Abstract Background Hormone receptor positive (HR+) breast cancer (BC) is the most common subtype of BC (70-80%). This subset tends to have good prognosis, therefore most patients with localized disease have excellent long-term survival, approaching 100% 5-year relative survival. However, 10% of patients experience loco-regional recurrence (LRR) within 5 year of final surgical management of the primary disease-well within the typical treatment window of adjuvant endocrine therapy. Few studies exists to guide the systemic treatment of patients who have suffered LRR of HR+ HER2 - BC. The randomized controlled CALOR trial demonstrated no benefit to systemic cytotoxic chemotherapy for this subgroup of patients and persistent high rate of subsequent recurrences (50% within 10 years on LRR event). There is no standard of care for managing this patient population. The combination of ribociclib and endocrine therapy (ET) (fulvestrant and aromatase inhibitors) is FDA approved for management of unresectable recurrences and metastatic HR+HER- BC (MONALEESA trials). CDK4/6 inhibitors have been investigated in early BC setting too, several trials showing positive results (monarchE, NATALEE). Data is needed to investigate their use in patients with LRR. Trial design This is a multicenter, single arm phase II study to evaluate efficacy and safety of ribociclib and ET in patients with LRR of HR+HER2- BC. Treatment includes ribociclib for 36 months, 600 mg daily for 21 days, 28-day cycle plus physician’s choice ET for 60 months (fulvestrant or AIs). Ribociclib dose was chosen based on approved dose in metastatic BC. Eligibility Criteria Patients ≥ 18 of age, with LRR of BC (ipsilateral breast, axilla, regional lymph nodes, chest wall), histologically confirmed estrogen receptor positive and/or progesterone receptor positive, HER 2 negative. Patients must have adequate local treatment for LRR (surgery and/or radiation) with negative microscopic margins, no evidence of distant metastatic disease. Prior treatment with neo-adjuvant and adjuvant chemotherapy and ET is allowed, no prior CDK 4/6 inhibitor in the last 12 months. Pre and post-menopausal women are allowed. Patient must enroll within 6 months of the last local therapy. Specific aims Primary objective: to estimate subsequent recurrence-free survival (RFS) at 3 years for ribociclib when administered with ET in patients with HR + HER2- BC with adequately resected local recurrence. Secondary objectives: to estimate distant metastasis-free survival and overall survival, to evaluate safety and tolerability, to identify predictors of LRR. Correlative analysis will explore prognostic and predictive biomarkers of treatment with ribociclib and ET and potential molecular mechanisms of resistance to treatment. Statistical Methods From previous published data (J Clin Oncol. 2018 Apr 10;36(11):1073-1079), we assume that patients receiving standard of-care management following recurrence would have a recurrence free survival (RFS) rate of 80% at 3 years and that treatment with ribociclib + ET will increase it by 7%. We wish to have at least 80% power at that significance level of 0.0487 to correctly detect that improvement in RFS rate at 3 years from 80 to 87%. Because only an improvement in RFS rate is of clinical interest, we have a directional hypothesis, and have used a 1-sided alpha. Using a one-sample survival study design, with assumed accrual duration of 3-years and additional follow-up time of 3 years, the minimum sample size requirement is N=180 patients. Target accrual The minimum sample size requirement is N=180 patients. A bigger sample size of N=200 patients will achieve a power of at least 84%. Current accrual is 6/200. This study will be open at up to 35 sites. Contact information The study is being administered through the HCRN, it can be identified as BRE20-468, NCT05467891, ocdanciu@uic.edu Citation Format: Oana Danciu, Nancy Chan, Kari Wisinski, Trish Millard, Kathleen Kemmer, Sneha Phadke, Zhengjia Chen, Ana Cuesta Fernandez, Melanie Clark, Alison Conlin, Coral Omene, Sima Ehsani, Stephanie Dublis, Vijayakrishna K. Gadi. A Phase II Study of Ribociclib and Endocrine Treatment of Physician’s Choice for Locoregional Recurrent, Resected Hormone Receptor Positive HER2 Negative Breast Cancer (RaPhLRR Study) [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 PO5-20-04.

e12569 Background: Triple-Negative Breast Cancers (TNBCs) represent a diverse subset of tumors characterized by varied responses to therapies including immunotherapy (IO). While IO is approved in early-stage and advanced TNBC, responses are modest. Modulation of the tumor microenvironment to improve responses to IO is an active area of research. In-vitro and in-vivo studies have shown Poly-ADP Ribose Polymerase inhibitors (PARPi) to increase PD-L1 expression in sporadic, BRCA1 and BRCA2 mutated TNBC cell lines improving response to IO. In addition, TNBCs have diverse mechanisms leading to Homologous Recombination Deficiency and the role of PARPi in sporadic TNBCs is still unclear. Methods: To further investigate the role of PARPi in tumor immuno-modulation we conducted a single-arm, open-label, window of opportunity (WOO) trial in patients with early-stage TNBC (NCT03911453). This study was approved by our institutional review board. Patients with histologically documented stage I-III TNBC were eligible for definitive surgery were enrolled. Patients were treated with 600mg BID rucaparib for 21 days. Pre- and post-treatment tumor biopsies were collected. Post-treatment, patients went to surgery or proceeded with neoadjuvant chemotherapy (NAC) followed by definitive surgery. Our primary endpoint was to assess change in PD-L1 expression. In addition, change in tumor microenvironment was by evaluating change in percentage of B cells, T cells and macrophages was calculated. Results: Twenty patients were enrolled. Nineteen patients completed 21 days and 1 patient went on extended duration PARPi during the COVID19 pandemic. Almost 50% of patients went to surgery while the rest went onto NAC after PARPi therapy. Pre-treatment tumor samples were obtained from the diagnostic core biopsies while post-treatment, fresh frozen and Formalin Fixed Paraffin Embedded were obtained either at time of surgery or a research biopsy prior to NAC initiation. Primary biomarkers data was successfully done in 14 paired samples. Treatment with rucaparib has increased expression of PD-L1 from median of 15% in pre-treatment tumor samples to a median of 26% in post-treatment tumor samples. Table below summarizes our results. Conclusions: Our study revealed that treatment with PARPi, rucaparib, changed the tumor microenvironment as noted by changes in expression of PD-L1, and immune milieu in and around the tumor. This could lead to change in responsiveness to therapies including CKI. This strategy should be further investigated to evaluate improving responses to immunotherapies. Clinical trial information: NCT03911453 . [Table: see text]

Introduction: Mammography is the cornerstone of breast cancer screening, diagnosis, and surveillance. After definitive treatment for breast cancer, mammograms are continued for surveillance. The current recommendations regarding surveillance after definitive treatment (surgery and radiation) lack consensus amongst various societies. There are no clear guidelines in regards to the type of mammogram recommended: diagnostic or screening mammogram or if a diagnostic mammogram is used, when to return to routine screening protocols. Current practice patterns are driven by physician’s preference. We conducted a survey to evaluate physicians’ preferences in ordering breast imaging post- breast cancer diagnosis and treatment. Methods: This survey was approved by University of Arizona institutional review board. This survey was conducted through American Society of Clinical Oncology (ASCO) voluntary opt-in Research Survey Pool (RSP). ASCO sent out this survey to 1000 randomly selected members between 10/19/2021-11/22/2021. Weekly reminders to participate were sent through the ASCO RSP for 5 weeks. Participants clicked the link to the survey platform where upon consent they completed the survey. Results: The survey was completed by 244 healthcare professionals through the ASCO RSP. Most respondents were physicians (n=228), primarily medical oncologists (n=174) and practiced in an academic environment in the United States (n=132). After definitive treatment, majority (58%) ordered first imaging at 6 months post-surgery/radiation, and it was primarily a diagnostic mammogram (68%). Interestingly, for patients at age 80 or above, screening mammogram was used for surveillance after definitive treatment by most respondents (59%). After first post-surgery/radiation mammogram there is an almost even spilt (50%) on continuing with diagnostic versus screening mammograms for follow up. Of those who order diagnostic mammograms, majority (38%) do it for 3-5 years with an additional 30% continuing it beyond 5 years. Almost 65% of respondents reported they do not stop screening mammograms at any age for patients with a history of early-stage breast cancer as long as they are healthy. Conclusions: The practice patterns of healthcare professionals as it relates to the type and frequency of breast imaging varies significantly. Despite having the same imaging quality there is a significant difference in the cost of screening and diagnostic mammograms. In addition, in clinical practice, most routine screening care is covered by insurances without co-pays or out of pocket costs for patients. Diagnostic imaging does not fall under routine screening care and frequently requires out of pocket expenses for patients. As insurance companies start to decline certain imaging modalities used for cancer detection due to lack of data supporting the use of these expensive studies, specific imaging guidelines for follow up in post-treatment setting for patients with breast cancer are needed. Citation Format: Meredith Whittaker, Kiah Farr, Preethika Potluri, Nova Foster, Jennifer Erdrich, Jennifer Segar, Sima Ehsani, Sao Jiralerspong, Denise Roe, Pavani Chalasani. Physician Practice Patterns of Breast Imaging After Treatment: Survey of Real-World Practice [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-05-04.

Purpose Bone metastases (BM) from breast cancer cause significant complications including pain, hypercalcemia, spinal cord compression, and pathologic fractures, collectively referred to as skeletal related events (SREs). Of all SREs, bone pain impacts the quality of life (QOL) most significantly. Cancer- induced bone pain (CIBP) is difficult to treat with limited treatment options and requires a multimodal approach. Management of CIBP is primarily by opioids which have notable side effects like sedation, constipation, and concern for addiction. In addition, pre-clinical evidence suggests that opioids accelerate bone loss and increase risk of fractures. There is an unmet need for novel analgesic therapy interventions to optimize QOL for patients with BM from metastatic breast cancer. Preclinical studies have shown that the endogenous cannabinoid (CB) system is involved in pain modulation, bone regulation, immunity, and restraint of cancer pathogenesis. CB2 receptor activation has been shown to inhibit proinflammatory cytokines/chemokines in pre-clinical models. Treatment with selective CB2 agonist in mice with BM led to significant antinociception, decreased cancer-induced bone degradation, and reduced side effects of morphine. In addition to alleviating pain, CB2 agonists were shown to enhance bone growth/strength in these mice. Based on this pre-clinical data, we hypothesized that the addition of a CB2 agonist will improve pain symptoms and decrease opioid requirement in patients with bone metastases from breast cancer. We proceeded to conduct a pilot study by repurposing a clinically approved CB2/CB1 agonist, dronabinol. Methods We conducted a prospective, single site study among patients with BM from breast cancer at our center (NCT03661892). Patients had to have been on opioids for CIBP for at least 4 weeks and not using marijuana or CBD products. Patients were treated with 10mg dronabinol BID for 8 weeks. Our primary objective was to determine the proportion who decrease their opioid use by ≥ 20%. The null hypothesis value was 5% of women would have a 20% decrease. With 14 participants, we could detect an increase from 5% to 29% (n=4) with 80% statistical power using a one-sided alpha level of 0.05. Participants completed Brief Pain Inventory and the European Organization for Research and Treatment of Cancer quality of life questionnaires pre and post treatment. Results Twenty participants consented with 14 patients completing the study and evaluable for primary analysis. No patients received any palliative radiation therapy or other therapies for bone pain within 3 months prior to enrollment to this study. Four patients decreased their opioid use by ≥ 20% meeting the primary objective. Patients reported significant improvement in pain severity, interference scores, quality of life and insomnia based on the questionnaires. There were no grade 4 side effects and only 1 patient had grade 3 adverse event (dizziness) related to study drug. Of the 14 patients who completed the study, 9 desired to continue dronabinol therapy after completion. Conclusion Our pilot study shows that the addition of dronabinol resulted in decreased opioid requirements for CIBP in patients with metastatic breast cancer. Patient-reported outcomes also demonstrated improved pain and QOL with the addition of dronabinol. While we did not see any significant AEs tolerability may be of concern due to CB1 psychoactive effects. Our results are promising and warrant further investigation into evaluating CB2 agonists for improved pain control from CIBP and to decrease opioid use. Citation Format: Jennifer Segar, Kiah Farr, Mary Junak, Denise Roe, Sima Ehsani, Sao Jiralerspong, Ibrahim Mohab, Todd Vanderah, Pavani Chalasani. Evaluation of Dronabinol to Decrease Opioid Use for Cancer- Induced Bone Pain [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-04-02.

Aromatase inhibitor-induced arthralgia (AIA) presents a major problem for patients with breast cancer but is poorly understood. This prospective study explored the inflammatory metabolomic changes in the development of AIA. This single-arm, prospective clinical trial enrolled 28 postmenopausal women with early-stage (0–3) ER+ breast cancer starting adjuvant anastrozole. Patients completed the Breast Cancer Prevention Trial (BCPT) Symptom Checklist and the Western Ontario and McMaster Universities Arthritis Index (WOMAC) at 0, 3, and 6 months. The plasma levels of four polyunsaturated fatty acids (PUFAs) and 48 oxylipins were quantified at each timepoint. The subscores for WOMAC-pain and stiffness as well as BCPT-total, hot flash, and musculoskeletal pain significantly increased from baseline to 6 months (all p < 0.05). PUFA and oxylipin levels were stable over time. The baseline levels of 8-HETE were positively associated with worsening BCPT-total, BCPT-hot flash, BCPT-musculoskeletal pain, WOMAC-pain, and WOMAC- stiffness at 6 months (all p < 0.05). Both 9-HOTrE and 13(S)-HOTrE were related to worsening hot flash, and 5-HETE was related to worsening stiffness (all p < 0.05). This is the first study to prospectively characterize oxylipin and PUFA levels in patients with breast cancer starting adjuvant anastrozole. The oxylipin 8-HETE should be investigated further as a potential biomarker for AIA.

240 Background: Chemotherapy induced alopecia (CIA) is known to have a significant psychological and quality of life impact, mainly in women. While cold caps have been shown to decrease CIA, expense, availability, and extension of treatment durations are barriers for routine clinical use. Keratinocyte Growth Factor (KGF) has been shown to have cytoprotective effects on human keratinocytes in vitro and reduce apoptosis in human hair follicles. Based on this data, we hypothesized that KGF-Hair serum (KGF-HS) will prevent CIA in women undergoing chemotherapy as treatment for breast cancer. Methods: We designed a Simon 2-stage prospective study to test our hypothesis. Study was approved by our institutional review board and registered on clinicaltrials.gov (NCT04554732). In part 1 we planned to enroll 20 patients into a single arm. If ≥ 4 responses are noted, we proposed to initiate part 2: randomized double-blind placebo-controlled study. Patients with early-stage breast cancer (ESBC) who were scheduled to get at least 4 cycles of anthracycline or taxane based chemotherapy were included. Patients with inflammatory scalp conditions, hair loss disorder, scalp disorders were excluded. The primary endpoint was successful hair preservation using the Common Terminology Criteria for Adverse Events 4.0 scale at the end of 4 cycles of chemotherapy. Secondary end points included wig use and scores on the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire–Core 30, Hospital Anxiety and Depression Scale, and a summary scale of the Body Image Scale. Results: Twenty patients completed part 1 of the study and were evaluable for primary endpoint. Mean age was 60 years and 70% were treated with taxane based chemotherapy. Successful hair preservation was noted in 0 of 20 women. Mean duration of treatment with KGF-HS was 4.6wks (range 2-10 weeks) before women came off study due to grade 2 hair loss. There were no statistically significant differences in changes in any of the scales of quality of life from baseline to end of treatment. There were only 2 grade 1 events (1 rash and 1 itching) reported which resolved after coming off the KGF-HS. There were no serious adverse device events. Conclusions: Among women with early-stage breast cancer receiving chemotherapy with a taxane, anthracycline, or both, using KGF-HS did not prevent CIA. Further research is needed to investigated other novel topical options to prevent CIA. Clinical trial information: NCT04554732.

Background C-C Chemokine Ligand type-5 (CCR5) is overexpressed in >95% of TNBC and has been correlated with disease progression. Moreover, enhancement of DNA repair signaling by CCR5 activation may contribute to chemotherapy resistance. Therefore, blocking CCR5 may result in increased immune response against tumor cells and synergize with chemotherapy. Leronlimab (PRO 140) is a humanized monoclonal antibody to CCR5. Preclinical data showed leronlimab binds human CCR5, blocks CCR5-mediated signaling, and CCL5-induced breast cancer cell invasion. The therapeutic antibody leronlimab has been administered to over 800 healthy and HIV-1 infected individuals with good tolerance and without obvious dose-related toxicity, making it an ideal partner for chemotherapy combinations in TNBC. Methods In this ongoing phase 1B/2 study, patients with CCR5+ mTNBC with ≤2 line of therapy in the metastatic setting (no prior carboplatin) are treated with weekly subcutaneous leronlimab (3 dose levels, 3+3 dose escalation) and a fixed dose of carboplatin AUC 5 on day 1 with a 21-day dose-limiting toxicity (DLT) window, followed by expansion in 30 patients with CCR5+ mTNBC who are naïve to chemotherapy in the metastatic setting or who have failed first-line combination of chemotherapy (excluding carboplatin) and a checkpoint inhibitor in the metastatic setting. CCR5 positivity is centrally assessed by IHC and defined as >10% CCR5 staining in primary or metastatic tumor cells and/or high predominance of CCR5+ tumor-infiltrating leukocytes (TIL). Primary objectives are safety, tolerability, determination of maximum tolerated dose, and determination of the recommended phase 2 dose (RP2D). Results Fifteen patients had archived tumor tissue assessed for CCR5 expression, with 12 being CCR5 positive (median expression 20%, range 0 - 100%, and 7 out of 12 high CCR5+ TILs) . A total of ten patients (median age 51 years; median 2 prior therapies) have been enrolled at 3 dose levels (350, 525, and 700 mg). In the second cohort, 1 additional patient was inadvertently enrolled. All patients completed the DLT assessment period and no DLTs have been observed. Patients received between 3 and 27 doses of leronlimab with the number of cycles ranging from 1 to 9. Five patients remain on treatment. The most common treatment-emergent adverse events (TEAEs) by any grade were: fatigue (6/10), headache (4/10), constipation (3/10), and nausea (3/10). The following grade ≥3 TEAEs were reported: neutropenia, anemia, thrombocytopenia, hyponatremia, hypertension, diarrhea and headache. Serious Adverse Events were reported in 2 patients (grade 2 sepsis and grade 3 headache). The following leronlimab treatment related adverse events (TRAEs) occurred (all grade 1): injection site reaction in cohort 1, fatigue (n=2) and headache in cohort 2. Three carboplatin TRAEs ≥3 were reported in one patient in cohort 1: thrombocytopenia, anemia and leukopenia. Two out of seven patients eligible for response achieved a confirmed partial response, and 4 patients stable disease. Conclusions Leronlimab, in combination with carboplatin, has been well-tolerated in all 3 dose levels with early signs of anti-tumor activity in patients with CCR5+ mTNBC. The study is currently enrolling patients at the RP2D dose of leronlimab 700mg in combination with carboplatin AUC 5 in the phase 2 part of the trial. Clinical trial information: NCT03838367 Citation Format: Massimo Cristofanilli, Namita Chittoria, Sima Ehsani, Hallgeir Rui, Milana Dolezal, Lisette Stork-Sloots, Femke de Snoo, Christopher Recknor, Vandana Abramson. A phase Ib/II study of leronlimab combined with carboplatin in patients with CCR5+ metastatic triple-negative breast cancer (mTNBC) [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 P5-17-08.