Prior Endocrine Therapy Research Articles

PSMA PET findings in an “EMBARK-like” cohort of patients with high-risk non-metastatic hormone-sensitive prostate cancer: A single center post-hoc retrospective analysis.

5091 Background: The EMBARK trial is a phase 3, randomized, study evaluating use of enzalutamide with or without concomitant leuprolide in non-metastatic castrate sensitive prostate cancer patients. Eligibility status for the trial relied upon conventional imaging which under detects metastatic disease in comparison to PSMA-PET imaging. The aim of this post-hoc retrospective analysis was to describe the PSMA-PET findings in a patient population representative of the EMBARK trial. Methods: This was a post-hoc, retrospective analysis of 5 prospective studies of PSMA PET conducted at UCLA from 2016 to 2021 that included patients with recurrent PCa following RP, RT or SRT. Patients were included if they met eligibility for enrollment in the EMBARK trial at the time of their PSMA scan defined as the following: Rising PSA at a level above 1.0ng/mL (post RP and SRT) or 2.0ng/mL > nadir (post-RT), PSA doubling time ≤ 9 months, Serum testosterone ≥ 150 ng/dL. Exclusion criteria constituted: distant metastatic disease as assessed by radiographic imaging, prior hormonal therapy or systemic therapy for prostate cancer. PSMA PET findings (PROMISE miTNM stage, number of lesions) were collected from the clinical imaging reports. Descriptive statistics were used (median, range). Results: From 2002 patients screened, 146 patients were included in the analysis. Median time from primary therapy to PSMA PET was 39 (2.1-261) months. Median pre-scan PSA levels and PSA doubling time in patients who underwent RP (n=85), dRT (n=22), post-RP SRT (n=39) and overall (n=146) were 2.4 ng/mL (1-72.1), 8.3 ng/mL (2.37-202), 2.58 ng/ml (1.1-32.3), 2.7 ng/mL (1-202), and 3.5 months (1-9), 3.3 months (1-9), 4.4 months (1-9), 3.7 (1-9) months, respectively. PSMA-PET was positive in 80%, 41%, 85%, 83% of the RP, dRT, RP + SRT and overall populations, respectively. Poly-metastatic disease (≥5 lesions) was found in 19%, 32%, 21% and 21% of cases, respectively. PSMA-PET detected disease only localized to the prostate fossa (miT+N0M0) in 7%, 32%, 0% and 9% respectively. PSMA-PET detected pelvic nodal disease (miTxN1M0) in 40% 18% 28% and 34% respectively. PSMA PET detected any distant metastatic disease (miTxNxM1) in 33%, 41% 56% and 40% respectively. PSMA-PET detected metastatic nodal only disease (N1 and/or M1a) in 58% 32% 74% and 39% and osseous disease (M1b) in 19% 23% 31% and 23% cases respectively. Conclusions: In this “EMBARK-like” cohort of patients with high-risk nmCS PCa and PSA DT < 9 months, PSMA PET was positive in 83% of patients, detected M1 disease in 40% of patients and over one-fifth of cases presented with 5 or more lesions. PSMA-PET provides novel additional risk stratification for patients with high-risk nmCS PCa without distant metastasis based on conventional imaging. Further studies are needed to assess its independent prognostic value and use for treatment guidance. Clinical trial information: NCT03582774 .

A phase 3 study of gedatolisib plus fulvestrant with and without palbociclib in patients with HR+/ HER2- advanced breast cancer previously treated with a CDK4/6 inhibitor plus a nonsteroidal aromatase inhibitor (VIKTORIA-1).

TPS1118 Background: Patients who receive frontline CDK4/6 inhibitor (CDK4/6i) therapy eventually experience disease progression. Resistance to CDK4/6i is likely a transient adaptive mechanism that may be reversed by inhibition of the PI3K/mTOR pathway. Thus, combination of CDK4/6i and PI3K/mTORi after disease progression on CDK4/6i could restore sensitivity to CDK4/6i and prevent activation of the PI3K/mTOR pathway. This hypothesis was evaluated in a Phase 1b study (Layman SABCS 2021) of gedatolisib (geda), a potent inhibitor of PI3K and mTOR. Subjects with HR+/HER2- ABC with prior CDK4/6i received geda (180 mg IV weekly for 3 weeks, then one week off) with palbociclib (palbo) and fulvestrant (FUL). Median PFS was 12.9 months with 63% overall response rate. Efficacy was observed regardless of PIK3CA mutation status (Wesolowski SABCS 2022). Geda was well tolerated, with few discontinuations due to treatment-related adverse events (4%). The most common AE was stomatitis; hyperglycemia of any grade occurred in 26% of patients. This preliminary data, dosing schedule, and study population characteristics form the basis for the Phase 3 trial, VIKTORIA-1 (NCT05501886). Methods: This Phase 3 multinational clinical trial will evaluate geda and FULwith or without palboin patients with HR+/HER2- ABC previously treated with any CDK4/6i in combination with a non-steroidal aromatase inhibitor (AI) therapy. Those without tumor PIK3CA mutations will be assigned to Study 1 (n=351) and randomized to Arm A (geda, palbo, and FUL), Arm B (geda and FUL), or Arm C (FUL). Those with PIK3CA mutations will be assigned to Study 2 (n=350) and randomized to Arm D (geda, palbo, and FUL), Arm E (alpelisib and FUL), or Arm F (geda and FUL). Key eligibility criteria include adults with confirmed metastatic or locally advanced breast cancer, any menopausal status, radiologically evaluable disease, and prior CDK4/6i treatment in combination with a non-steroidal AI. Prior hormonal therapy, including SERDs, is allowed. Key exclusion criteria include prior treatment with a PI3K, Akt, or mTOR inhibitor, prior treatment with chemotherapy for advanced disease, more than two lines of prior endocrine therapy, bone only disease with no soft tissue components, active CNS metastases, and type 1 diabetes or uncontrolled type 2 diabetes. The primary endpoint is PFS assessed by blinded independent central review per RECIST v1.1. Secondary endpoints included overall survival, safety and tolerability, ORR, duration of response, time to response, CBR, quality of life, and pharmacokinetics. The trial is open for enrollment. Clinical trial information: NCT05501886 .

TROPiCS-03: A phase 2 basket study of sacituzumab govitecan (SG) in patients (pts) with metastatic solid tumors—Early analysis in pts with advanced/metastatic endometrial cancer (EC).

5610 Background: Pts with advanced/metastatic EC who progressed on or after platinum (PT)-based and anti–PD-(L)1 therapies have a poor prognosis with limited treatment options. SG is a Trop-2–directed antibody-drug conjugate. In the open-label, phase 1/2 IMMU-132-01 basket study, SG monotherapy resulted in a 22% objective response rate (ORR) with a manageable safety profile in 18 pts with metastatic EC who had relapsed after or were refractory to ≥1 prior standard therapeutic regimen (Bardia et al. Ann Oncol. 2021). Here, we report early data in pts with advanced/ metastatic disease from the EC cohort of the TROPiCS-03 Ph2 study. Methods: TROPiCS-03 (NCT03964727) is a multicohort, open-label, Ph 2 basket study in pts with metastatic solid tumors. Adult pts in the EC cohort progressed after prior PT-based chemotherapy and anti–PD-(L)1 directed therapy [requirement for PD-(L)1 progression added in amendment], had ECOG PS 0-1 and creatinine clearance ≥30 mL/min. Pts received 10 mg/kg of SG on D1 and D8 of a 21-D cycle. The primary endpoint was ORR by investigator’s assessment per RECIST 1.1. Secondary endpoints included duration of response (DOR), clinical benefit rate (CBR), and progression-free survival (PFS) per investigator’s assessment, overall survival, and safety. The safety population included pts who received ≥1 dose of SG; the efficacy population included pts receiving ≥1 dose of SG and had ≥13 weeks of follow-up. Results: As of data extraction on October 11, 2022, 28 pts received ≥1 dose of SG. Median study follow-up was 5.3 mo (range, 0.4-13.1); median age 69 y (range, 44-83), 57% ECOG PS 1,14% microsatellite instability high. Pts received a median of 3 prior therapies (range, 1-6); 100% received prior PT-based chemotherapy, 61% prior immunotherapy, 54% prior targeted agents, and 11% prior hormonal therapy. In 20 pts with ≥13 weeks of follow-up, ORR was 25% (95% CI, 8.7-49.1). Regarding best overall response, all responses were partial response (PR). In addition, stable disease (SD) was 40% and progressive disease was 15%; CBR (confirmed complete response + PR + SD ≥ 6 mo) was 35% (95% CI, 15.4-59.2). Median PFS was 5.6 mo (95% CI, 2.3 mo-not reached [NR]) and median DOR was NR (95% CI, 2.76 mo-NR; n = 5). Treatment was ongoing for 50% of pts. Grade ≥3 treatment-related adverse events (TRAEs) occurred in 64% of pts; most common grade ≥3 TRAEs were neutropenia (25%), febrile neutropenia (14%), and diarrhea (14%). Discontinuation rate due to TRAEs was 7%. While on treatment, two deaths occurred due to causes unrelated to SG. Conclusions: Preliminary findings showed encouraging efficacy of SG with a manageable toxicity profile in a pretreated population with advanced/metastatic EC. Safety signals were consistent with the known SG safety profile. This early analysis will be updated with the full dataset. Clinical trial information: NCT03964727 .

Tolerability and preliminary activity of the potent, selective, oral CDK7 inhibitor SY-5609 in combination with fulvestrant in patients with advanced hormone receptor-positive (HR+), HER2- breast cancer (BC).

3081 Background: SY-5609 is an oral, reversible, potent, and selective inhibitor of CDK7, a key regulator of transcription and cell cycle, currently under investigation in a Phase 1 study in patients (pts) with select advanced solid tumors (NCT04247126). Single agent (SA) dose escalation is ongoing, using a 7 days on/7 days off (7/7) dosing schedule that optimized tolerability (Sharma 2021) and showed a correlation of antitumor activity with higher exposures. SY-5609 may address multiple CDK4/6 inhibitor resistance mechanisms and potentiates SERD activity in CDK4/6 inhibitor-resistant xenograft models (Johannessen 2019). In this Phase 1 study, it was combined with the SERD fulvestrant in advanced HR+, HER2- BC pts who are refractory to CDK4/6 inhibitor + hormonal therapy. Methods: Evaluation of SY-5609 + fulvestrant began with a SY-5609 dose that had cleared the SA dose-limiting toxicity (DLT) evaluation period. SY-5609 was dosed once daily at 3 mg or 4 mg on a 21 days on/7 days off (21/7), 5 days on/2 days off (5/2), or 7/7 schedule and was escalated using a 3+3 design, guided by safety and reports of Cycle 1 qualifying safety events (QSEs), which matched SA DLT criteria. Fulvestrant was dosed at the approved dose/schedule. Safety and tolerability of SY-5609 + fulvestrant and SY-5609 PK were secondary objectives. Exploratory objectives included preliminary antitumor activity (RECIST v1.1.). Results: As of 12 Oct 2022, 14 pts (median age 63; range 46 - 83) received SY-5609 at 3 mg on a 21/7 schedule (n=8) or at 4 mg on a 5/2 (n=5) or 7/7 (n=1) schedule in combination with fulvestrant. Pts had advanced disease, including 79% with liver lesions, and a median of 5.5 (range 2 - 12) prior therapies; 100% had prior hormonal therapy, including 71% who received prior fulvestrant. The majority of adverse events (AEs) were low-grade and reversible. Related AEs (≥10%) included nausea, diarrhea, fatigue, thrombocytopenia, and hot flush. Related ≥Grade 3 AEs were reported in 3 pts (21%), including 1 QSE of Grade 3 thrombocytopenia at 4 mg 5/2. The highest tolerated dose in combination with fulvestrant was not reached. Stable disease (SD) was observed in 5/12 (42%) evaluable pts. SD with tumor shrinkage and/or SD >6 months was observed in 4 pts previously treated with fulvestrant and in pts with liver lesions and/or TP53 mutations. SY-5609 exposure in combination with fulvestrant appeared comparable to SA at Day 1. Conclusions: SY-5609 + fulvestrant has an acceptable safety profile consistent with SA SY-5609 or fulvestrant. The mechanistic rationale for CDK7 inhibition in HR+, HER2- BC and the tolerability and encouraging early activity in this heavily pretreated population support future investigation of SY-5609 in combination with SERDs, including defining the maximum tolerated combination dose using the 7/7 SY-5609 schedule. Clinical trial information: NCT04247126 .

Lasofoxifene (LAS) plus abemaciclib (Abema) for treating ESR1-mutated ER+/HER2- metastatic breast cancer (mBC) after progression on prior therapies: ELAINE 2 study update.

1057 Background: Endocrine therapy (ET), particularly aromatase inhibitors (AIs), for estrogen receptor (ER)-positive breast cancer can lead to acquired ESR1 mutations ( mESR1) driving endocrine resistance and tumor progression. Treatments for mBC with mESR1 are limited, especially after progression on ET/cyclin-dependent kinase 4 and 6 inhibitor (CDK4/6i) combinations. In ELAINE 2, LAS, a next-generation ET (breast ER antagonist) plus Abema had a median progression-free survival (PFS) of ~13 mos, objective response rate (ORR) of 33%, and 24-wk clinical benefit rate (CBR) of 62% with a favorable safety profile in patients with resistant mESR1 mBC (Damodaran S, et al. J Clin Oncol. 2022;40:16 suppl 1022). Here, we report ELAINE 2 data with longer patient follow up (Jan 31, 2023). Methods: In this open-label, phase 2, single-arm study, 29 women with mESR1, ER+/HER2- mBC that progressed on prior ET took oral LAS 5 mg/day and Abema 150 mg BID until disease progression/toxicity. The primary endpoint was safety/tolerability; secondary included PFS, CBR, and ORR. Data were summarized descriptively with no formal hypothesis testing. Results: Patients (median age 60 yrs) had received a median of 2 prior therapy lines for mBC; all but one had prior CDK4/6i exposure and 14 (48%) had prior chemotherapy for mBC. LAS/Abema was well tolerated with primarily grade 1/2 treatment-emergent adverse events (most commonly diarrhea, nausea, fatigue, and vomiting). One treatment withdrawal occurred due to grade 2 diarrhea. No deaths occurred. LAS dose was not reduced; Abema dose was reduced to 100 mg BID in 6 (21%) patients. Median PFS was 56.0 wks (~13 mos) and CBR 65.5% (95% CI, 47.3‒80.1). Median overall survival was not estimable. In 18 patients with measurable lesions, ORR was 55.6% (95% CI, 33.7‒75.4), with median time to response of 5.7 mos and median duration of response of 6.4 mos. Seventy-six percent, 56%, and 39% of patients were progression free at 6, 12, and 18 mos, respectively. Three (10%) patients had scan-identified venous thromboembolic events, with one symptomatic pulmonary embolism and one symptomatic deep vein thrombosis. In 26 patients with evaluable baseline and wk 4 ctDNA, ESR1 mutant allele fraction decreased from baseline to wk 4 in 81% of patients and was not detected in 54%. Conclusions: With longer ELAINE 2 follow up, LAS/Abema continues to be well tolerated with clinically meaningful efficacy in women with mESR1, ER+/HER2- mBC that had progressed on ET and CDK4/6is. Decreases in mESR1 ctDNA suggest effective target engagement of LAS. The PFS (median ~13 mos) and ORR (56%) with LAS/Abema are promising and a confirmatory phase 3 study (ELAINE 3) will begin in 2023. If ELAINE 2 results are confirmed, the combination of LAS and Abema would address a critical unmet need, providing a practice changing option for treating mESR1 breast cancer. Clinical trial information: NCT04432454 .

First-in-human phase 1/2a study of a potent and novel CDK2-selective inhibitor PF-07104091 in patients (pts) with advanced solid tumors, enriched for CDK4/6 inhibitor resistant HR+/HER2- breast cancer.

3010 Background: PF-07104091 is a novel CDK2-selective inhibitor under investigation in pts with selected advanced or metastatic solid tumors. We present the first disclosure of data from the first-in-human, multicenter, phase 1 study of PF-07104091 monotherapy (NCT04553133). Methods: Pts with HR+/HER2- advanced/metastatic breast cancer (mBC) who received ≥ 2 lines of treatment for mBC including prior endocrine therapy (ET) + CDK4/6 inhibitors (CDK4/6i), and pts with other solid tumors, were included. Prior therapy with fulvestrant and chemotherapy was allowed for pts with mBC. PF-07104091 (75-500 mg) was given twice daily (BID) orally in 28-day cycles, following Bayesian design with overdose control, to determine the maximum tolerated dose (MTD)/recommended dose for expansion (RDE). Primary objective was to assess safety and tolerability. Secondary objectives included pharmacokinetics and preliminary anti-tumor activity. Results: At data cut off (Aug 23, 2022), 35 pts with advanced solid tumors (n = 29 mBC) with median age 62y (range 32-80y), median 4 lines of prior systemic therapy (range 1–12) and ECOG PS 0 (20% pts) or 1 were enrolled. Of 29 pts with mBC, all had prior CDK4/6i, 25 (86.2%) prior fulvestrant, and 21 (72.4%) prior chemotherapy. Treatment-emergent adverse events (TEAEs) were observed in 34 pts (97.1%; 20 [57.1%] grade [G] ≥ 3). The most frequent TEAEs (all G≤3) were nausea (77.1%; 14.3% G3), diarrhea (48.6%; 8.6% G3), vomiting (48.6%; 2.9% G3), fatigue (45.7%; 20.0% G3) and anemia (45.7%; 8.6% G3). Dose-limiting toxicity occurred in 5 pts: 1 pt (G3 fatigue) at 300 mg BID; 2 pts (1 G3 nausea and G3 anorexia, 1 G3 nausea) at 375 mg BID, and 2 pts (1 G3 fatigue and 1 G3 diarrhea) at 500 mg BID. Steady-state PF-07104091 plasma exposures increased proportionally with dose. A trend of early decrease in ctDNA was observed. Further pharmacodynamic studies are ongoing. PF-07104091 300 mg BID was identified as the MTD and selected as the monotherapy RDE. Among 16 response evaluable mBC pts (all prior CDK4/6i+ET) with measurable disease at baseline, confirmed RECIST v1.1 partial responses were observed in 3 (18.8 %) pts (2 pts with duration of response > 6 months and 1 ongoing at data cut off), and stable disease in 6 (37.5%) pts. Disease control rate was 61.5% in mBC pts (response evaluable set, 95% CI: 40.6, 79.8). Conclusions: Treatment with PF-07104091 monotherapy was generally well tolerated and showed antitumor activity in heavily pretreated HR+ HER2- mBC pts who progressed on prior CDK4/6i. Dose expansions of PF-07104091 are ongoing as monotherapy in pts with ovarian cancer and in combination with fulvestrant in pts with breast cancer. Clinical trial information: NCT04553133 .

In brief: A new breast cancer indication for sacituzumab govitecan (Trodelvy).

Sacituzumab govitecan-hziy (Trodelvy – Gilead) has been approved for treatment of unresectable locally advanced or metastatic hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer in adults who received prior endocrine therapy and ≥2 additional systemic therapies for metastatic disease. It was previously approved for treatment-refractory metastatic triplenegative breast cancer and for treatment of locally advanced or metastatic urothelial cancer in adults who received platinum-based chemotherapy and a programmed death receptor-1 (PD-1) or programmed death-ligand 1 (PD-L1) inhibitor.

Abstract PD13-11: PD13-11 Final Overall Survival Analysis of Monarch 2 : A Phase 3 trial of Abemaciclib Plus Fulvestrant in Patients with Hormone Receptor-Positive, HER2-Negative Advanced Breast Cancer

Abstract Background Abemaciclib is approved for patients (pts) with hormone receptor-positive (HR+), HER2-negative (HER2-) advanced breast cancer (ABC) with progression on prior endocrine therapy (ET). The MONARCH 2 trial showed a statistically significantly benefit in progression-free survival (PFS) (hazard ratio [HR]: 0.553; 95% CI: 0.449-0.681; p < 0.001), overall survival (OS) (HR: 0.757; 95% CI: 0.606-0.945; p = 0.01) and a manageable safety profile for abemaciclib plus fulvestrant compared with fulvestrant alone. Here we report the pre-specified final overall survival (OS) analysis from the MONARCH 2 trial (NCT02107703). Methods MONARCH 2 was a global, randomized, placebo-controlled, double-blind phase 3 trial of abemaciclib or placebo, plus fulvestrant for treatment of pre-, peri- or postmenopausal women with CDK 4 & 6 inhibitor naïve HR+, HER2- ABC that progressed during ET. Pts were randomized 2:1 to receive abemaciclib or placebo, 150 mg twice daily, plus fulvestrant. Randomization was stratified based on site of metastasis (visceral, bone only, or other) and resistance to prior ET (primary versus secondary). OS and safety were key secondary endpoints, and chemotherapy-free survival was an exploratory endpoint defined as the time from randomization to initiation of chemotherapy or death, whichever occurs the earliest. Kaplan-Meier (KM) method was used to analyze time-to-event variables. A stratified Cox proportional hazards model was used to estimate treatment effect hazard ratio (HR). The prespecified final analysis was planned to occur based on approximately 441 OS events. Data cutoff was March 18, 2022. Results 669 women were randomized 2:1 to receive abemaciclib (n = 446) or placebo (n = 223), plus fulvestrant. Baseline characteristics have been previously reported (Sledge et. al., Jama Oncol 2020). The median follow-up time was approximately 80 months and at the time of the data cutoff, 11% of pts were still receiving study drug in the abemaciclib arm versus 2% in the placebo arm. 440 OS events were observed in the ITT population (abemaciclib arm: 283 events; placebo arm: 157 events). The median OS was 45.8 months in the abemaciclib arm and 37.2 months in the placebo arm (HR: 0.784; 95% CI: 0.644-0.955). The maintained separation of the KM curves beyond the medians is illustrated by the differences in the estimated 5- and 6-year OS rates between arms (5-year: 41.2% versus 29.2%; 6-year: 34.7% versus 23.7%; abemaciclib versus placebo respectively). While OS benefit was generally consistent across subgroups, a more pronounced benefit is noted in subgroups associated with a poorer prognosis such as visceral disease (HR: 0.643; 95% CI: 0.499-0.829), primary resistance to ET (HR: 0.634; 95% CI: 0.436-0.922) or negative progesterone receptor status (HR: 0.623; 95% CI: 0.405-0.959). Moreover, the addition of abemaciclib to fulvestrant deferred the initiation of chemotherapy (HR: 0.674; 95% CI: 0.562-0.809), with substantial difference in yearly chemotherapy-free survival rates (3 year: 42% vs 29.3%; 4 year: 37% vs 18.6%; 5 year: 32.4% vs 14.7%). Notably with longer exposure to abemaciclib, no new additional safety risks or cumulative toxicities were identified. Conclusions At the prespecified final OS analysis of the MONARCH 2 trial, with a median follow-up of 6.5 years, the statistically significant benefit previously demonstrated was confirmed and maintained. OS benefit was generally consistent across subgroups, with numerically greater effect size observed among patients with poorer prognosis. Importantly, the survival benefit came with a substantial extension of the chemotherapy-free survival time, which is an important consideration for pts with ABC. The results also provide assurance of the safety of abemaciclib with longer-term use. Citation Format: Antonio Llombart-Cussac, George Sledge, Masakazu Toi, Patrick Neven, Joo Hyuk Sohn, Kenichi Inoue, Xavier Pivot, Meena Okera, Norikazu Masuda, Peter A. Kaufman, Han Koh, Eva-Maria Grischke, PierFranco Conte, Valerie Andre, Yuanyuan Bian, Ashwin Shahir, Gertjan van Hal. PD13-11 Final Overall Survival Analysis of Monarch 2 : A Phase 3 trial of Abemaciclib Plus Fulvestrant in Patients with Hormone Receptor-Positive, HER2-Negative Advanced Breast Cancer [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 PD13-11.

Abstract OT2-01-02: The SMILE Study: A phase II trial of onapristone in combination with fulvestrant for patients with ER-positive and HER2-negative metastatic breast cancer after progression on endocrine therapy and CDK 4/6 inhibitors

Abstract Background Antiprogestins, including selective progesterone receptor (PgR) modulators (SPRMs) that act as PgR antagonists, are a promising class of therapeutics for overcoming endocrine resistance including in patients who develop activating estrogen receptor alpha (ESR1) mutations after prior endocrine therapy (ET). The SMILE study is a multi-institutional phase II clinical trial to determine the efficacy and safety of an antiprogestin, onapristone in combination with fulvestrant as second-line therapy for patients with ER+,PgR+/-, HER2 -metastatic breast cancer (MBC). Methods Patients with locally advanced or MBC who progress on ≥2 lines of prior therapy with ET as a single agent or in combination with CDK4/6 inhibitors, mTOR inhibitors and one line of chemotherapy in the metastatic setting are eligible. Other criteria include ECOG performance status ≤ 2, measurable disease per RECIST 1.1 criteria, adequate organ function, availability of an archived tumor biopsy block confirming the diagnosis of MBC, optional biopsy at disease progression on trial, and optional 18F-fluorofuranylnorprogesterone (18F-FFNP) PET/CT imaging. Ovarian suppression is allowed. Prior ET with tamoxifen or aromatase inhibitor therapy in the adjuvant or metastatic setting is allowed. Patients with prior exposure to fulvestrant, antiprogestins, or CDK inhibitors in the adjuvant setting are ineligible. Following consent, all subjects will receive fulvestrant at the recommended dosing schedule plus onapristone 50 mg orally, twice daily, until disease progression, unacceptable toxicity, or discontinuation for any other reason. Using the Simon Two-Stage design, a total of 39 patients will be enrolled over two years from 6-8 sites within Wisconsin Oncology Network (WON); study enrollment began in November 2021. In the first stage of the trial, thus far, nine patients were accrued who are tolerating the trial regimen well with no reported toxicities or serious events. The safety monitoring is planned when the cohort size reaches eleven patients, and interim analysis at 21 patients; if ≥2 responses are observed, then 18 additional subjects will be enrolled in the second stage. This design yields a one-sided type I error rate of 5% if the ORR is 7% and power of 80% when the combination’s true response rate is 20%. The primary objective is to evaluate the objective response rate; secondary objectives include safety and tolerability, progression-free survival, disease control rate, and duration of response. Other correlates include optional functional imaging of PgR binding with 18F-FFNP PET/CT and biomarker analysis (ER, total PgR, HER2, Ki67, CD24, CD44, LDH1, KLF4, CK 5/6, PhosphoSer294-PgR on tissue samples, ESR1 mutations, and circulating tumor DNA analysis). Citation Format: Sailaja Kamaraju, Amy Fowler, Lubna N. Chaudhary, Mark Burkard, Thomas Giever, Robert N Hegeman, Michele Pipp-Dahm, Yee Chung Cheng, Carol Lange, Julie M. Jorns, Amy Stella, Nauman Siddiqui, Luke Zurbriggen, Saurabh Rajguru, Sergey Tarima, Deepika Sriram, Janet Retseck, Hallgeir Rui, Tarek Sahmoud, Kari B. Wisinski. The SMILE Study: A phase II trial of onapristone in combination with fulvestrant for patients with ER-positive and HER2-negative metastatic breast cancer after progression on endocrine therapy and CDK 4/6 inhibitors [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 OT2-01-02.

Abstract P5-02-23: Association of Neutrophil-to-Lymphocyte Ratio and Absolute Lymphocyte Count with Clinical Outcomes for Patients with Advanced Breast Cancer in the MONARCH 2 Trial

Abstract Background: Pretreatment neutrophil-to-lymphocyte ratio (NLR) and absolute lymphocyte count (ALC) are putative prognostic factors in patients with advanced breast cancer (ABC). Little information is available on the prognostic value of these immune status markers in patients treated with abemaciclib (ABE). In this study, we investigated the relationship between baseline NLR and ALC and clinical outcomes using data from the phase 3 MONARCH 2 (M2) trial. Methods: The M2 study compared ABE/fulvestrant to placebo (PBO)/fulvestrant in patients with estrogen-receptor positive, human epidermal growth factor receptor 2-negative ABC that had progressed on prior endocrine therapy. The current post hoc analyses used baseline laboratory data and outcome data from the June 20, 2019, cutoff date (median follow-up: 47.7 months). For both baseline NLR and baseline ALC, patients were divided into high and low categories, defined by a cutoff of 2.5 for NLR and 1.5 × 109/L for ALC. The association of baseline NLR and ALC with investigator-assessed progression-free survival (PFS) and overall survival (OS) was explored using Cox models stratified by treatment and described using Kaplan-Meier estimates. After assessing the prognostic value of baseline NLR and ALC for PFS and OS using a univariate analysis, a multivariate model was used to determine whether baseline NLR and ALC were independently prognostic considering additional baseline and disease characteristic factors. Results: Data were available for 426 and 219 patients in the ABE and PBO arms, respectively. Median baseline NLR was 2.5 and 2.4 in the ABE and PBO arms, respectively. Median baseline ALC was 1.4 × 109/L in both arms. The numbers of patients categorized into the high and low categories were well balanced for analysis of both NLR and ALC. Univariate analyses showed that baseline NLR (< 2.5, ≥2.5) was a prognostic factor for PFS and OS (2-sided p< 0.0001). Patients with low baseline NLR consistently had better PFS and OS than those with high baseline NLR, and the treatment effect of ABE against PBO was consistently observed regardless of NLR category (Table 1). Univariate analyses showed that baseline ALC (< 1.5 × 109/L, ≥1.5 × 109/L) was also a prognostic factor for PFS and OS (2-sided p=0.0116 and 0.0032, respectively). PFS and OS were better for patients with high baseline ALC than for those with low baseline ALC, and the treatment effect of ABE against PBO was observed regardless of ALC category (Table 1). For PFS, the multivariate model was adjusted for Eastern Cooperative Oncology Group performance status (ECOG PS), tumor grade, presence of liver metastasis, and bone-only disease. For OS, the multivariate model was adjusted for sensitivity to endocrine therapy, ECOG PS, presence of liver metastasis, and bone-only disease. When adjusting for these additional prognostic factors, baseline NLR, but not baseline ALC, remained statistically significant in the multivariate model (2-sided p< 0.0001). Conclusions: These exploratory analyses suggest that while both baseline NLR and ALC are prognostic of clinical outcomes, only baseline NLR is independently prognostic of PFS and OS. Low baseline NLR was associated with better PFS and OS outcomes, but the benefit of adding ABE to fulvestrant was similar regardless of baseline NLR status. Table 1. Summary of outcomes by treatment arm for NLR and ALC categories ALC, absolute lymphocyte count; CI, confidence interval; NLR, neutrophil-to-lymphocyte ratio; NR, not reached; OS, overall survival; PFS, progression-free survival. Citation Format: Eriko Tokunaga, Yasuo Miyoshi, Koji Dozono, Tsutomu Kawaguchi, Masakazu Toi. Association of Neutrophil-to-Lymphocyte Ratio and Absolute Lymphocyte Count with Clinical Outcomes for Patients with Advanced Breast Cancer in the MONARCH 2 Trial [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 P5-02-23.

Abstract P3-07-15: Preliminary data from a Phase 1b dose escalation study of OP-1250, an oral CERAN, in combination with palbociclib in patients with advanced and/or metastatic estrogen receptor (ER)-positive, HER2-negative breast cancer

Abstract Background: OP-1250 is a small molecule oral complete estrogen receptor antagonist (CERAN) that binds the ligand binding domain of the ER and completely blocks ER-driven transcriptional activity. CDK4/6 inhibitors in combination with endocrine therapy have improved progression free survival and overall survival for patients (pts) with metastatic breast cancer (MBC) in the first- and second-line settings. However, most patients will progress and newer combinations such as with OP-1250 may provide improved clinical outcome. OP-1250 potently inactivates both wild-type ER and mutant forms of ER. The latter confers ligand independent activity and is a mechanism of resistance to standard of care endocrine therapies. In preclinical studies, OP-1250 in combination with palbociclib demonstrated synergistic activity in models of wild-type ER and those containing ESR1 activating mutations, and in models of brain metastasis. A Phase 1/2 monotherapy study of OP-1250 is ongoing in MBC subjects who have received 1 or more prior endocrine therapies (NCT04505826). Monotherapy is well tolerated and the recommended phase 2 dose is 120 mg QD. The aim of this combination trial is to define the maximum tolerated dose (MTD), safety, tolerability, and pharmacokinetics (PK) of OP-1250 in combination with palbociclib. Methods: Eligibility criteria include pts with MBC or locally advanced breast cancer who have received no more than 1 prior line of endocrine therapy (prior CDK4/6 inhibitors and one line of chemotherapy are permitted) and measurable or non-measurable disease. Using a 3+3 design, cohorts are sequentially enrolled, and pts receive escalating doses of OP-1250 orally QD continuously in combination with 125 mg of palbociclib orally for 21 of 28 days. Pts are evaluable for dose limiting toxicities (DLTs) if >75% of both treatments were administered within the first 28-day treatment cycle. Blood is collected for PK on cycle 1 days 1, 2 and cycle 2 days 15, 16 for OP-1250 and cycle 1 day 15 for palbociclib. PK profiles, exposure parameters, and drug-drug interactions (DDIs) are assessed. Pts are monitored for adverse events (AE) and tumor assessments (RECIST 1.1) are conducted every two cycles. Results: As of July 7, 2022, 9 pts were evaluable for DLTs after 28 days of treatment in dose levels 30 mg, 60 mg, and 90 mg of OP-1250 in combination with palbociclib. No DLTs occurred at any of the dose levels. As of May 13, 2022, of the 7 pt safety data set, the most common Grade 1/2 treatment emergent adverse events (TEAE), which occurred in 2 patients, were nausea, gastroesophageal reflux, vomiting, and fatigue. Grade 3 neutropenia occurred in 4 pts and all were attributed to palbociclib by the investigator. No Grade 4 events were observed. OP-1250 was highly bioavailable and showed dose proportional exposure in combination with palbociclib. The single and multiple dose exposure of OP-1250 was consistent with that observed in the monotherapy study, indicating an absence of effect of palbociclib on OP-1250 PK. 90 mg steady-state evaluation is ongoing. Palbociclib concentrations at steady state did not demonstrate a meaningful difference from published exposure parameters for the three dose levels evaluated, indicating an absence of DDI. Conclusions: In the first three cohorts of OP-1250 and palbociclib, the combination was well tolerated and no DLTs occurred. There were no clinically significant DDIs observed between OP-1250 and palbociclib at the doses evaluated and exposure of each drug was consistent with observed monotherapy exposure levels. Dose escalation of OP-1250 continues to 120 mg, to be followed by dose expansion. Updated data will be presented. (NCT05266105) Citation Format: Arlene Chan, Daphne Day, Rina Hui, Nicole McCarthy, Rosalind Wilson, Demiana Faltaos, Morena Shaw, Caitlin Murphy. Preliminary data from a Phase 1b dose escalation study of OP-1250, an oral CERAN, in combination with palbociclib in patients with advanced and/or metastatic estrogen receptor (ER)-positive, HER2-negative breast cancer [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 P3-07-15.

Abstract P4-07-54: Health related quality of life of patients treated with bevacizumab and paclitaxel as first-line treatment for HER2 negative metastatic breast cancer: impact of clinical factors

Abstract Background: Advances in screening and treatment have led to increase in breast cancer (BC) survival in recent years but prognoses for metastatic BC remain poor with poorer outcomes as health-related quality of life (HRQOL). Treatment as bevacizumab and paclitaxel for metastatic BC, although that can increase time to progression of disease, often carry toxicity and is not curative but rather palliative in intent with the goal to improve or maintain HRQOL. The aim of this work was to assess impact of clinical factors such as disease progression, toxicity on HRQOL. Methods: COMET study is a multicenter prospective single-arm cohort study in France whose main objective was to identify biological factor that could predict the clinical benefit of bevacizumab-paclitaxel combination therapy as first treatment in HER2 negative metastatic BC. HRQOL was assessed at baseline, at every cycle (every for 4 weeks) until progression and then every 3 months up to death using the EORTC QLQ-C30 questionnaire and its BC specific module, the EORTC QLQ-BR23. In this ancillary study, we targeted 5 dimensions HRQOL for the primary analyses: Global health status (GHS), physical functioning (PF), Emotional functioning (EF), fatigue (FA) and pain (PA). The primary endpoint was time until definitive deterioration (TUDD) in HRQOL scales that defined as time between inclusion and the first decrease HRQOL score ≥ 5 points compared to baseline score, with no further improvement of at least 5 points. Multivariable Cox model with time dependent covariate was performed to assess clinical factors associated with TUDD for each of the 5 target dimensions HRQOL. We performed 3 models for each dimension: model 1 including all covariate with p< 0.10 in univariable; model 2 including model 1 and adjusted on cancer subtype and model 3 included model 1 stratified by cancer subtype. P value < 0.01 were considered statistically significant. Results: Out of 510 patients included in COMET study, 432 patients with available HRQOL data were analyzed in this study. Median age at inclusion was 58 years (range: 29-83), and 24.4% of patients had triple negative tumor subtype. About 79 % of cancers were invasive ductal carcinoma and 43 % patients had least 3 metastasis sites at baseline. At baseline, patients reported a mean score for GHS of 57.6 (SD=22.7), for PF of 75.8 (23.2), for EF of 62.2 (25.8), for FA of 42.2 (29.60) and for PA of 38.1 (31.5). The Median TUDDs for the 5 targeted dimensions was 10.1 months [7.5-16.9] for GHS, 6.1 months [4.1-8.9] for PF, 21.6 [18.7-31.2] for EF, 10.8 [6.2-16.6] for FA and 13.6[10.1-22.5] months for PA. In multivariable analyses, Disease Progression was associated with TUDD of GHS (HR [99%CI] =2.4 [1.2-4.9] and TUDD of PF (2.1 [1.1-3.7]). After adjusted on cancer subtype, association persisted with TUDD of GHS (p=0.009). Performance Status was associated with TUDD of PF (1.6 [1.2-2.3]), and TUDD of Pain (1.6 [1.1-2.3]). Performance Status association with TUDD of PF continued after adjustment on cancer subtype (p=0.0003). Prior endocrine therapy was associated with TUDD of pain in patients with tumor with positive hormone receptor (HR+) (2.4 [1.2-4.7]). There was no factor associated with TUDD of EF and TUDD of FA. Conclusion: Results of this study have shown that among the 5 targeted dimensions HRQOL, Physical Functioning was deteriorated in the shortest time. Disease progression, base line performance status and prior endocrine therapy for HR+ subtype, are clinical factors that could influence HRQOL in HER2 negative metastatic BC treated with first line chemotherapy. Citation Format: Oumar Billa, Sandrine Dabakuyo, Marion Chevrier, Franck Bonnetain, Isabelle Desmoulins, William Jacot, Olivier Trédan, Marc Debled, Christelle Levy, Anthony Gonçalves, Jean-Marc Ferrero, Florence Dalenc, Christelle Jouannaud, Marie-Ange Mouret-Reynier, Mireille Mousseau, Julien Grenier, Jean-Philippe Jacquin, Fatima-Zohra Toumi, Frédérique Berger, Jérôme Lemonnier, Jean-Yves Pierga. Health related quality of life of patients treated with bevacizumab and paclitaxel as first-line treatment for HER2 negative metastatic breast cancer: impact of clinical factors [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 P4-07-54.

Abstract P3-01-03: Characterization of neutropenia in patients with hormone receptor–positive/human epidermal growth factor receptor 2–negative (HR+/HER2–) advanced breast cancer on palbociclib in a real-world setting: Results from POLARIS

Abstract Background: The cyclin-dependent kinase 4/6 inhibitor palbociclib (PAL) is approved for the treatment of HR+/HER2– advanced breast cancer (ABC) in combination with an aromatase inhibitor (AI) as initial endocrine-based therapy or with fulvestrant (FUL) in patients whose disease progressed on prior endocrine therapy (ET). In clinical trials, the most common any-grade adverse event (AE) associated with PAL treatment was neutropenia. Here we evaluated the incidence of and risk factors for neutropenia by treatment cycle and line of therapy (LOT), as well as incidence of dose modification due to neutropenia, in patients with HR+/HER2– ABC receiving PAL in a real-world setting. Methods: POLARIS is a prospective, noninterventional, multicenter, real-world study of patients with HR+/HER2‒ ABC receiving PAL in routine clinical practice in the United States and Canada. Per protocol, sites were instructed to report absolute neutrophil count at baseline, anytime during the first 3 cycles, then at Day 1 (or before the start of a new cycle) of subsequent cycles per standard of care or as needed up to 6 months. The safety analysis set included all patients enrolled in the study who received at least one dose of study medication.Results: As of March 30, 2022, 1242 patients had enrolled in the study (median age, 64.0 years; 98.8% female; 94.8% stage IV; 39.1% visceral disease). Of these, 902 (72.6%) patients received PAL as first LOT and 340 (27.4%) as second LOT or greater. Among all patients, 722 received PAL + AI, 487 PAL + FUL, and 33 PAL + none or other ET (other than letrozole, anastrozole, fulvestrant, or exemestane); 90% of all patients started with 125 mg of PAL in the first cycle. Incidence of neutropenia among patients receiving PAL by cycle and LOT is shown in the Table. Percentages of patients experiencing on-treatment neutropenia were similar regardless of LOT. Over the course of treatment grade ≥3 neutropenia and febrile neutropenia were reported in 16.1% and 0.8% patients, respectively, and 19.2% of patients experienced a decreased neutrophil count. A total of 337 (27.1%) had a dose modification due to neutropenia. Of these 337 patients, 190 (56.4%) had a dose reduction associated with neutropenia. Conclusions: In this real-world study, incidences of treatment-related neutropenia associated with PAL were consistent with those reported in randomized clinical trials and were manageable by dose modification. Febrile neutropenia was uncommon. Incidences of neutropenia reported within the first 6 months were comparable among patients regardless of LOT. Further research is needed to understand the impact of the incidence of and risk factors for treatment-related neutropenia on therapy.Clinical trial identification: Pfizer; NCT03280303 Citation Format: Debu Tripathy, Joanne L. Blum, Bethany Sleckman, Kamal Patel, Ibrahim Nakhoul, Eric Gauthier, Monica Z. Montelongo, Zhe Zhang, Yao Wang, Gabrielle B. Rocque. Characterization of neutropenia in patients with hormone receptor–positive/human epidermal growth factor receptor 2–negative (HR+/HER2–) advanced breast cancer on palbociclib in a real-world setting: Results from POLARIS [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 P3-01-03.

Abstract PD13-07: PD13-07 Combination therapy with the AKT inhibitor, ipatasertib, endocrine therapy, and a CDK4/6 inhibitor for hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC): results from the phase I TAKTIC trial

Abstract Background: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) provide significant clinical benefit in patients with HR+/HER2- metastatic breast cancer (MBC) and have become a standard of care treatment. Prior insights from tumor profiling and preclinical analyses suggest that AKT1 activation can induce CDK4/6i resistance. We hypothesized that targeting AKT1 following CDK4/6i progression may be an effective therapeutic strategy and conducted a clinical trial to evaluate both doublet (ET+AKTi) and triplet (ET+AKTIi+CDK 4/6i) therapy in the ≥ 2nd line MBC setting. Methods: TAKTIC is an open-label phase Ib clinical trial (clinicaltrials.gov NCT03959891) evaluating the combination of the AKT inhibitor ipatasertib (ipat) with fulvestrant (Arm A), an aromatase inhibitor (Arm B), or the triplet combination (Arm C) with fulvestrant + palbociclib (palbo). The primary objective is to evaluate the safety (NCI CTCAE 5.0) and tolerability of ipat in combination with endocrine therapy +/- CDK4/6i. Secondary objectives include clinical efficacy, as determined by objective response rate (RECIST v1.1), clinical benefit rate (CBR), progression-free survival (PFS), and overall survival (OS). Key inclusion criteria include unresectable HR+/HER2- MBC; at least 1 prior therapy for MBC including any CDK4/6i; up to 2 prior lines of chemotherapy for MBC (no limit on prior endocrine therapy). Here, we present an updated interim analysis from all study arms. Results: The trial completed accrual with 77 pts enrolled from June 2019 – February 2022, including 19 on Arm A, 16 on Arm B, and 42 on Arm C. Median age was 62 (range 32-88) and 65/77 pts (84%) received prior CDK4/6i (median no. of prior lines = 3, range 1-13). 56/77 pts (73%) had measurable disease at baseline and 50/77 pts (65%) had visceral metastases in the liver/lung (68% Arm A, 44% Arm B, 71% Arm C). Pts enrolled on Arms A and B received ipat at 400mg in combination with fulvestrant or an aromatase inhibitor, respectively. In Arm C, 27/42 pts enrolled into the dose escalation phase and received ipat + palbo at varying doses in combination with fulvestrant. Two DLTs were observed in the 300mg ipat + 125mg palbo cohort (grade 4 neutropenia ≥ 7 days). ET+400mg ipat + 100mg palbo was determined to be the recommended phase 2 dose (R2PD), and the remaining 15/42 pts on Arm C were treated at this dose level in the expansion phase. Treatment was well tolerated in all arms. Grade 3 and 4 toxicities included neutropenia (39/77, 50.6%), leukopenia (15/77, 19.5%), diarrhea (11/77, 14/3%), transaminitis (7/77, 9.1%), lymphopenia (6/77, 7.8%), rash (6/77, 7.8%), and thrombocytopenia (3/77, 3.9%). As of 6/28/2022, 16/77 pts remain on treatment. The median treatment duration for all pts is estimated at 6 months (range 0.5-39). Among the 56 pts with measurable disease, 11 had partial response (PR) and 32 had stable disease (SD) as the best response. CBR, defined as percentage of pts who achieved PR or SD > 6 months, was 48% across the study (53% Arm A, 31% Arm B, 57% Arm C). The median PFS was 5.5 months (95% confidence interval [CI]: 3.8 – 7.4) and the median OS was 24.5 months (95% CI: 17.1 – 33.9). Conclusions: The combination of ipat with endocrine therapy +/- palbo is well tolerated in heavily pre-treated pts, with preliminary evidence of clinical activity. This trial demonstrates how molecular insights related to CDK4/6i resistance inform potential therapy combinations. Further studies are needed to evaluate AKTi-based combinations in pts with HR+ MBC. Citation Format: Seth A. Wander, Jennifer C. Keenan, Andrzej Niemierko, Dejan Juric, Laura M. Spring, Jeffrey Supko, Neelima Vidula, Steven J. Isakoff, Lianne Ryan, Sarah Padden, Elizabeth Fisher, Amber Newton, Beverly Moy, Leif Ellisen, Douglas S. Micalizzi, Aditya Bardia. PD13-07 Combination therapy with the AKT inhibitor, ipatasertib, endocrine therapy, and a CDK4/6 inhibitor for hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC): results from the phase I TAKTIC trial [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 PD13-07.

Abstract OT1-11-01: Phase II study of talazoparib, a PARP inhibitor, in somatic BRCA1/2 mutant metastatic breast cancer identified by cell-free DNA or tumor tissue genotyping

Abstract Background: PARP inhibitors are currently approved for the treatment of germline BRCA1/2 mutant metastatic breast cancer (MBC), which accounts for 5-10% of breast cancer. We hypothesize that a PARP inhibitor may also have efficacy in somatic BRCA1/2 mutant MBC, expanding the potential clinical applicability of PARP inhibitors. We previously demonstrated that somatic BRCA1/2 mutations can be identified by both cell-free DNA and tumor tissue genotyping in a subset of patients with MBC who are not germline BRCA1/2 carriers. Furthermore, a PARP inhibitor was demonstrated to induce cell growth inhibition in a circulating tumor cell culture model generated from a patient with pathogenic somatic BRCA1 mutant MBC (Vidula, Dubash, CCR, 2020). In this trial, we are evaluating the efficacy of a PARP inhibitor in somatic BRCA1/2 mutant MBC. Trial Design: This phase II investigator-initiated clinical trial is enrolling 30 patients with somatic BRCA1/2 mutant MBC identified via cell-free DNA or tumor tissue genotyping. Patients are treated with talazoparib, a PARP inhibitor, until disease progression. At baseline and every 3 months, patients undergo CT chest, abdomen, and pelvis, and a bone scan for disease assessment. Patients undergo blood collection at baseline for the Cancer Risk B (CR-B) assay, a novel flow variant assay to assess double-strand break repair mutations in circulating blood cells (Syeda, 2017) and monthly blood collection for cell-free DNA analysis to evaluate changes in the genomic environment. Eligibility Criteria: Patients with MBC with a pathogenic somatic BRCA1/2 mutation identified by cell-free DNA or tumor tissue genotyping are eligible. Both patients with triple-negative breast cancer (≥ 1 prior chemotherapy) or hormone receptor positive/HER2- MBC (≥ 1 prior hormone therapy) are eligible. Patients should not be known germline BRCA1/2 carriers. There is no limit on prior therapies including receipt of a prior platinum (in the absence of disease progression on prior platinum). A prior PARP inhibitor is not allowed. Adequate performance status and organ function are needed. Specific Aims: Primary aim is progression-free survival (PFS) assessed by RECIST 1.1. Secondary aims include objective response rate and toxicity assessed by NCI CTCAE v 5.0. Exploratory aims include assessing impact of BRCA1/2 reversion mutations in cell-free DNA, studying serial changes in BRCA1/2 mutant allelic frequency in cell-free DNA, comparing pre- and post-treatment cell-free DNA results to identify changes in the genomic environment, assessing the CR-B assay positivity rate, and correlating these biomarker analyses with patient response. Statistical Methods: This study uses a two-stage design with 80% power to demonstrate that talazoparib is associated with “success” (PFS > 12 weeks) in 53% patients (4% alpha). Accrual: This study (NCT03990896) is open at Massachusetts General Hospital, MD Anderson, University of California San Francisco, and Emory, with pending activation at Northwestern, Cornell, and Vanderbilt. Five patients are enrolled as of 7/2022. Funding: This study is supported by a Pfizer ASPIRE award and Conquer Cancer Foundation of ASCO–Breast Cancer Research Foundation- Career Development Award. Contact information: Neelima Vidula, MD, Massachusetts General Hospital, nvidula@mgh.harvard.edu Citation Format: Neelima Vidula, Senthil Damodaran, Erica L. Blouch, Nora Horick, Nathan Royce Ruffle-Deignan, Manali Bhave, Ami N. Shah, Leticia Varella, Vandana Abramson, Joseph Sparano, Leif Ellisen, Ishraq Alim, Harry Ostrer, Hope Rugo, Aditya Bardia. Phase II study of talazoparib, a PARP inhibitor, in somatic BRCA1/2 mutant metastatic breast cancer identified by cell-free DNA or tumor tissue genotyping [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 OT1-11-01.

Abstract P3-05-28: Impact of increased adiposity on extended aromatase inhibitor treatment in postmenopausal patients with estrogen receptor positive (ER+) breast cancer: a retrospective analysis of the SOLE trial

Abstract Background: The risk of late distant recurrence (≥ 5 years) in post-menopausal patients with ER+ BC remains significant even after standard adjuvant endocrine therapy (ET). Obesity, which has reached high proportions in Western Countries, is one of the modifiable factors that can contribute to BC recurrences. While body mass index (BMI) is an easily available surrogate measure of adiposity, it might not reflect accurately patient adiposity, especially in post-menopausal patients. We therefore hypothesize that mammary adipocyte measurements might better capture the adiposity of the patient. In this study, we retrospectively evaluated the prognostic role of both BMI and adipocyte measurements in the SOLE trial. Patients & Methods: The SOLE trial (NCT00553410) consisted of 4,884 postmenopausal women with hormone receptor positive, lymph node-positive BC treated with 5 years of letrozole after having completed 4-6 years of adjuvant ET. BMI was available for 3,606 patients with ER+/HER2- BC and categorized according to the WHO classification (underweight: < 18.5, normal weight 18.5 – 24.9, overweight 25 – 29.9, obesity ≥ 30 kg/m2). Considering the small sample size, patients with underweight (n=35) were grouped together with patients with normal weight for the subsequent analyses. We evaluated the association between clinico-pathological characteristics and BMI using Fisher exact test and Kruskal-Wallis test. Given the previously reported association of BMI with distant recurrences (PMID: 21115856), we considered distant-relapse free interval (DRFI) as the main study endpoint. Cox regression analyses were adjusted for histology, chemotherapy (yes/no), type of local therapy, in addition to previously reported clinico-pathological variables (PMID: 29158011). Then, we conducted a stratified case-cohort study consisting of 311 patients (97 with distant relapse-cases) with successful digital assessment of adipocytes on normal mammary adipose tissue sample collected at surgery, as previously described (PMID: 33120083). Stratification factors were treatment arm and type of prior ET. Weighted Cox regression models (PMID: 17554753, 18712477) were used to evaluate prognostic association with adipocyte size (area in µm²) categorized in quartile of the 75th percentile (Q4 vs Q1-3), as done previously (PMID: 33753731). Results: 1392 (39%) patients were normal weight, 1315 (36%) were overweight and 899 (25%) were obese. Older age at diagnosis, lymph node involvement (≥4), large tumor size and menopausal status were associated with overweight and obesity. After a median follow-up of 84 months, no associations were found between DRFI and BMI in the univariable and multivariable analysis (adjusted HR overweight vs normal=0.99, 95%CI: 0.76 – 1.29, p=0.977 and HR obese vs normal=1.11, 95%CI: 0.84 - 1.47, p=0.425). In the case-cohort study, patients with larger adipocytes had an increased hazard of distant recurrence in the univariable and multivariable analysis (see table 1). Conclusion: In this study, we did not detect any association between BMI and survival outcomes. We however found that larger mammary adipocytes were independently associated with an increased hazard of distant recurrence. These results suggest that mammary adipocytes, which can be easily evaluated on H&E slides using digital pathology, should be considered as a novel marker to evaluate the risk of late recurrence in patients with breast cancer. Citation Format: Edoardo Isnaldi, François Richard, Giuseppe Marano, Patrizia Boracchi, Marion Maetens, Giuseppe Floris, Guy Jerusalem, Andrea Gombos, Alastair M. Thompson, Erika Hitre, Stefan Aebi, Marco Colleoni, Patrizia Dell’Orto, Roswitha Kammler, Patrick Neven, Giuseppe Viale, Meredith Regan, Elia Biganzoli, Christine Desmedt. Impact of increased adiposity on extended aromatase inhibitor treatment in postmenopausal patients with estrogen receptor positive (ER+) breast cancer: a retrospective analysis of the SOLE trial [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 P3-05-28.

Abstract OT2-03-02: lidERA Breast Cancer: A phase III adjuvant study of giredestrant (GDC-9545) vs physician’s choice of endocrine therapy in patients with estrogen receptor+, HER2– early breast cancer

Abstract OT2-03-02: lidERA Breast Cancer: A phase III adjuvant study of giredestrant (GDC-9545) vs physician’s choice of endocrine therapy in patients with estrogen receptor+, HER2– early breast cancer

Abstract P5-05-02: Estrogen receptor 1 (ESR1) mutations in circulating tumor DNA (ctDNA) from patients with ER+/HER2- metastatic breast cancer (mBC) treated with lasofoxifene plus abemaciclib in the ELAINE 2 study

Abstract Introduction: Use of long-term endocrine therapy (ET) for ER+ breast cancer often leads to acquired ESR1 mutations (mutESR1), causing endocrine resistance, tumor progression, and poor prognosis. An unmet clinical need exists for treating ER+ mBC patients with mutESR1, particularly after progression on CDK4/6 inhibitors (CDK4/6i). ELAINE 2 is an open-label, phase 2, multicenter trial evaluating safety and efficacy of lasofoxifene (LAS [selective estrogen receptor modulator]) plus abemaciclib (Abema [CDK4/6i], provided by Eli Lilly) in patients with ER+/HER2- and mutESR1 mBC who progressed after prior ET. Preliminary data with LAS plus Abema showed median progression-free survival of 55.7 wks, objective response rate of 50%, and 24-wk clinical benefit (CB) rate of 69%, with an acceptable safety and tolerability profile. Here, we report ESR1 ctDNA mutant allele frequency (MAF) and correlations of ESR1 MAF changes with CB. Methods: ELAINE 2 patients with detectable ctDNA mutESR1 at baseline (BL) were analyzed. Oral LAS 5 mg/day and Abema 150 mg BID were taken until disease progression, death, unacceptable toxicity, or withdrawal from the study. ctDNA was assessed by the Sysmex-Inostics SafeSeq assay—which detects mutESR1 at low allele fractions—at BL, every 4 wks, and end of treatment. MAF changes from BL to wk 4 were characterized as decreased (decrease in ESR1 MAF or none detected [ND]), increased (increase in MAF), or equivocal (in polyclonal patients [>1 mutESR1] with some MAF increasing and decreasing trends). Correlations of MAF change at 4 wks with CB at 24 wks were explored. Results: 29 patients (median of 2 prior metastatic therapies: 97% CDK4/6i, 79% fulvestrant, 48% chemotherapy) had BL mutESR1 of Y537S (66%), D538G (45%), Y537N (28%), and other less frequently detected mutations; 14 (48.3%) patients were polyclonal. 26 of 29 patients had evaluable BL and wk-4 ctDNA results: 21 patients had decreased MAF (81% [54% with ND]), 3 (12%) had increased, and 2 (8%) had equivocal ESR1 MAF changes (Table). CB at 24 wks was seen in 17 patients with a decrease, 2 with an increase, and 1 with equivocal MAF change. A sensitivity of 89.5% and specificity of 20% were calculated for predicting CB based on direction of ESR1 MAF change. The positive predictive value (PPV) for CB with decreased MAF was 81% and the negative predictive value (NPV) for an increased MAF was 33%. Of the 14 (54%) patients with ND ESR1 MAF, 13 had CB resulting in 87% sensitivity, 50% specificity, 93% PPV, and 33% NPV. Conclusion: In ELAINE 2, 81% of patients had decrease/cleared (ND) mutESR1 after 4 wks of LAS plus Abema, which correlated with clinical benefit. All mutESR1 detected appear targeted with this therapy. High sensitivity and favorable PPV were observed in patients with decreased MAF, and even more so in those with ND MAF; however, increased MAF was less specific and not as predictive of treatment failure. Our results indicate that ESR1 liquid biopsy evaluation may be an adequate non-invasive surrogate marker for monitoring patients on treatment. Further study in a larger population of women with endocrine-resistant mBC and acquired mutESR1 is warranted to explore this potential for monitoring treatment response or resistance to this novel LAS-Abema combination. Table. Change from baseline to week 4 in ESR1 MAF and clinical benefit at 24 weeks. CI, confidence interval; MAF, mutant allele fraction; ND, none detected; NPV, negative predictive value; PPV, positive predictive value. *Sensitivity and specificity analyses do not include equivocal results. Citation Format: Senthil Damodaran, Halle Moore, Ciara C. O’Sullivan, Paul V. Plourde, Gary Riordan, Hillary S. Sloane, Debu Tripathy, Dominic Carroll, David J Portman. Estrogen receptor 1 (ESR1) mutations in circulating tumor DNA (ctDNA) from patients with ER+/HER2- metastatic breast cancer (mBC) treated with lasofoxifene plus abemaciclib in the ELAINE 2 study [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 P5-05-02.

Abstract PD17-08: Pooled gene expression analysis and association with treatment response in patients with HR+/HER2− advanced breast cancer in the MONALEESA-2, -3, and -7 trials

Abstract Background: The Phase III MONALEESA (ML)-2, -3, and -7 trials showed significant improvement in progression-free survival (PFS) and overall survival (OS) with ribociclib (RIB) + endocrine therapy (ET) over placebo (PBO) + ET in patients (pts) with HR+/HER2− advanced breast cancer (ABC); improvement in OS with cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) has been observed in some, but not all clinical trials. Gene expression analyses for each separate ML study were reported previously. Given the differences in CDK4 vs CDK6 inhibition between RIB and other CDK4/6i, we evaluated the association between cell cycle (CC)–related genes and outcomes based on pooled analysis of gene expression using tumor samples from the ML-2, -3, and -7 trials. Methods: Gene expression data were generated from pre-treatment archival tumor samples (primary, 73%; metastatic, 27%) with a customized NanoString nCounter panel (781 genes) including genes involved in CC, other signaling pathways, and breast cancer biology. Samples were pooled from 1139 pre- and postmenopausal pts with HR+/HER2− ABC across the 3 ML studies, which included pts on first- and second-line therapy. Data were categorized into training (80%) and test (20%) datasets. The training dataset was used to analyze each gene (modeled continuously) individually for an association with PFS, and genes with a gene × treatment (tx) interaction P value <.10 were evaluated in the test dataset. Genes or gene signatures were classified by tertiles based on expression level (low/medium/high). For each tertile, median (m) PFS was calculated by the Kaplan-Meier method, and hazard ratios (HRs) of tx benefit (RIB vs PBO) were estimated. A Cox proportional hazards model adjusting for clinical covariates was used. A machine learning approach (elastic net survival model with stability selection), which used available gene expression data and select clinical factors and their interactions with tx arms, was applied to predict PFS. Results: This report focused on CC-related genes and signatures. Gene expression levels of CDKN2B and the expression ratio of CCND1/CDKN2A showed a predictive relationship with benefit from RIB in both training and test sets (Table). PFS benefit with RIB was consistent regardless of the CDK4/CDK6 expression ratio or level of expression of CCNE1, CDK2, RB1, combined CC-related genes, E2F gene signatures, RB gene signature, combined DNA-replication genes, or combined proliferation-related genes. A machine learning approach identified a clinico-genomic signature that was prognostic for PFS benefit with RIB. Selected variables included gene expression levels of FXBO5, PGR, RBBP8, and STC2 and several clinical features (tx arm, de novo disease, prior ET, and visceral disease). Pts with a low signature score had a longer mPFS vs pts with a high signature score, in the RIB (HR, 0.37; 95% CI, 0.22-0.62) and PBO (HR, 0.30; 95% CI, 0.15-0.59) arms. Conclusion: In the largest pooled analysis of the association of gene expression profile data with CDK4/6i tx response in pts with HR+/HER2− ABC, the PFS benefit with RIB + ET over ET alone was consistent irrespective of expression levels of most CC genes. Variation in magnitude of RIB benefit was observed, depending on CDKN2B expression levels, CCND1/CDKN2A expression ratio, and machine learning–derived signature scores. The clinico-genomic CDK4/6i signature requires validation in additional datasets. Table 1: Progression-Free Survival by Gene Expression Subgroup Citation Format: Aditya Bardia, Faye Su, Nadia Solovieff, Fabrice Andre, Carlos Arteaga, Patrick Neven, Yoon-Sim Yap, Yen-Shen Lu, Stephen K. Chia, Dennis Slamon, Seock-Ah Im, Arunava Chakravartty, Agnes Lteif, Tetiana Taran, Debu Tripathy. Pooled gene expression analysis and association with treatment response in patients with HR+/HER2− advanced breast cancer in the MONALEESA-2, -3, and -7 trials [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 PD17-08.

Abstract P5-08-05: Conception and Pregnancy Among Young Breast Cancer Survivors

Abstract Background: Breast cancer (BC) is the most common malignancy among women of reproductive age. Given limited data describing the conception and pregnancy experience of young BC survivors, we sought to explore these outcomes to inform counseling of women interested in future childbearing. Methods: Participants with stage 0-III BC in the Young Women’s Breast Cancer Study (NCT01468246), a multi-center, prospective cohort of women diagnosed at age ≤ 40 from 2006-2016 who reported ≥ 1 live birth from a pregnancy after diagnosis were sent a survey with investigator-developed questions focused on their first post-diagnosis live birth. Women who had been diagnosed with BC during pregnancy were excluded from this analysis. The survey assessed conception, use of assisted reproductive technology (ART), pre-implantation genetic testing (PGT), endocrine therapy (ET), and peripartum complications. Summary statistics are presented. Results: 92/119 eligible women completed the survey (response rate: 77%). Median age at diagnosis was 32 (range:17-40) years and at delivery was 37 (range: 29-47) years. Median time from diagnosis to delivery was 58 months (range: 11-154). Most women had stage 2 BC (43%, 40/92); 68% received chemotherapy (63/92); about half (51%, 47/92) were nulligravida at diagnosis. Overall, 61% of pregnancies were conceived naturally (56/92) and 39% with ART (36/92): 32% by in-vitro fertilization (IVF, 29/92), 7% with fertility medications only (6/92), and 1 with intrauterine insemination. 38% of IVF pregnancies were conceived using products from fertility preservation prior to BC treatment (11/29). Among women who used ART, 74% attempted to conceive naturally (25/36) for a median of 9 (range: 2-48) months prior to pursuing ART. The most common reasons for pursuing ART include infertility following BC treatment (33%, 12/36) and expediting conception to resume treatment (17%, 6/36). 11% of those with known inherited pathologic variant mutations underwent PGT (2/19). Reasons for not pursuing PGT included belief in more effective cancer risk reduction in the future (29%, 5/17), not being offered PGT (24%, 4/17), high cost (12%, 2/17), no interest in IVF (12%, 2/17), acceptable odds for inheriting the mutation (24%, 4/17), and belief in other risk reduction strategies (18%, 3/17); 1 woman reported ethical concerns. Of 57 women who took ET pre-pregnancy (63%), nearly all (96%, 55/57) discontinued ET > 3 months prior to attempting to conceive; 1 discontinued after awareness of pregnancy. Of those who had received prior ET, 60% resumed ET (34/57) a median of 3 (range: 1-50) months after pregnancy. Among 23 women who did not resume, 13 (23%) had completed the recommended duration; the remaining 10 reported one or more of the following reasons: felt better while off (28%, 6/23), desire for another child (22%, 5/23), and desire to breastfeed (17%, 4/23). Median time to delivery was 39 (range: 28-42) weeks with 12% delivering preterm < 37 weeks (11/92). 47% had a Caesarean section (43/92), with prolonged labor the most common indication (33%, 14/43). Hypertensive disorders of pregnancy (HDP, 20%, 18/92), gestational diabetes (7%, 6/92), small for gestational age (7%, 6/92), and postpartum hemorrhage (5%, 5/92) were the most common obstetrical complications. 9% of women had newborns requiring NICU admission (8/92) and 9% had low birth weight (8/92). Conclusion: Among young BC survivors with a live birth following diagnosis, most conceived naturally, with the majority who used ART first attempting natural conception. There was limited use of PGT among mutation carriers with ¼ not having been offered testing. Patient reported peripartum complications appear consistent with population norms, though the relatively higher rate of HDP bears further research. Among those yet to complete their ET, a notable proportion did not resume following delivery. This novel data may help to inform the care of young breast cancer survivors pursuing pregnancy. Citation Format: Kimia Sorouri, Tal Sella, Shoshana Rosenberg, Margaret Loucks, Kathryn Ruddy, Shari I. Gelber, Rulla M. Tamimi, Jeffrey M. Peppercorn, Lidia Schapira, Virginia F. Borges, Steven E. Come, Ellen Warner, Ann Partridge. Conception and Pregnancy Among Young Breast Cancer Survivors [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 P5-08-05.