Chen, Nan

The NCCN Clinical Practice Guidelines for Breast Cancer include recommendations for clinical management of patients with carcinoma in situ, invasive breast cancer, Paget’s disease, Phyllodes tumor, inflammatory breast cancer, and management of breast cancer during pregnancy. The panel convenes annually to update recommendations based on a review of recently published clinical trials. This selection from the NCCN Guidelines for Breast Cancer focuses on the recommendations for the management of recurrent or stage IV (M1) metastatic breast cancer. It summarizes the treatment strategies stratified by tumor biology, including hormone receptor status and HER2 expression, as well as clinical factors such as prior therapy and disease-free interval. Throughout all treatment lines, supportive care, quality of life preservation, toxicity minimization, and clinical trial participation are emphasized as integral components of patient care.

The treatment landscape of invasive early-stage and metastatic breast cancer is evolving constantly. These NCCN Guidelines Insights focus on recent updates included in the most recent version (version 5.2025) of the NCCN Guidelines for Breast Cancer specific to workup, locoregional therapy, surveillance, and systemic neoadjuvant/adjuvant therapy recommendations for invasive, nonmetastatic breast cancer.

604 Background: The addition of OFS to standard endocrine therapy (ET) improves iDFS for preM women with early-stage hormone receptor positive (HR+) breast cancer (BC). Incomplete OFS occurs in a subset of women, the long-term clinical significance of which is unclear. This study evaluates local sE2 levels in preM women receiving OFS with an oral SERD in the neoadjuvant (NA) setting. Methods: The EOP is a I-SPY2 sub-study investigating NA endocrine-based strategies in pts with HR+ HER2- Stage 2/3 BC predicted to have lower benefit from chemotherapy. Pts were randomized to oral amcenestrant 200 mg/d, alone or in combination with either letrozole 2.5 mg/d or abemaciclib 150 mg bid. Additional pts were randomized to a standard of care (SOC) arm consisting of an aromatase inhibitor. All PreM pts received OFS with monthly GnRHa up to 2 wks prior to C1D1 of study therapy. Pts were treated for 6 months prior to surgery. sE2 levels were collected locally prior to each GnRHa injection. Tumor Ki67 was assessed at 3 weeks and surgery, and associated with sE2 level. Statistical significance was determined using a two-sided Student’s t-test and a significance level 0.05. Results: Between 5/2021-8/2022, 74 pts were enrolled to an amcenestrant containing arm, 40 of whom were preM. 38/40 pts had at least one local sE2 level measured in follow up. Of these 38 pts (median age 45 years), 37 suppressed sE2 into the postmenopausal (postM) range at one or more follow-up timepoints. Of the 37 pts that completely suppressed into the postM range, 6 pts had sE2 levels rebound into the preM range (mean 319 pg/mL, range 20-848 pg/mL) with peak sE2 levels occurring at a median of 12 weeks from C1D1. One pt never suppressed to the postM range (peak sE2 1227 pg/mL) and was found to have an ovarian cyst after 3 months on amcenestrant, requiring surgery. One additional pt had multiple ovarian cysts (sE2 84 pg/mL). Median age of the 7 pts who had sE2 rebound was 43 years. There was no significant difference in Ki67 at 3 weeks and surgery between pts whose sE2 levels remained suppressed (median Ki67 2.0%) compared to those whose estradiol rebounded into the preM range or never suppressed (median Ki67 1.5%). In the 5 pts whose sE2 rebounded to > 200 pg/mL, all pts had tumor Ki67 < 10% at 3 weeks and surgery. Between 12/2022 and 8/2023, 20 pts were enrolled to AI +/- OFS and 11 pts were preM. Of the 11 preM pts, all pts suppressed sE2 to the postM range. No SOC patients had sE2 levels rebound into the preM range. Conclusions: In this study of neoadjuvant oral SERD with monthly OFS, 7/38 (18.4%) preM pts had sE2 levels remain or rebound into the preM range. sE2 levels did not appear to impact Ki67 suppression on NA ET. Work up for ovarian cysts should be considered in pts with symptoms, or significantly elevated or persistent sE2 levels. Clinical trial information: NCT01042379 .

612 Background: EOP, an I-SPY2 sub-study, evaluates the tolerability and activity of novel endocrine strategies in stage 2/3 breast cancer (BC) patients (pts) predicted to have lower chemotherapy benefit. Laso, a selective estrogen receptor modulator (SERM), has shown favorable toxicity profile and activity in HR+/HER2- endocrine-resistant metastatic BC. Methods: Pts with Stage 2/3 HR+/HER2-, MammaPrint (MP) low risk BC were enrolled. Pts with MP High1 BC were included if clinically node-negative. Pts received oral laso 5 mg daily for six 28-day cycles. Laso was continued until the day prior to surgery. Premenopausal pts received ovarian function suppression (OFS) starting C2D1. The primary endpoint was feasibility (>75% of patients completing >75% study therapy). Baseline (T0), 3-wk (T1) biopsies, and the surgical specimen (T3) was assessed centrally for Ki-67. Breast MRI functional tumor volume (FTV) was performed at T0, T1, 12 weeks (T2), and pre-operatively (T3). Blood was collected for tumor informed ctDNA at T0, T1, T2, T3. Advance event (AE) was assessed using CTCAE V5. Results: From 3/2023 to 5/2024, 20 pts were enrolled. Median age 50.5 years, 50% premenopausal, and 1 male pt. 60% cN0, 80% MP low-risk signature. 18 (90%) pts completed >75% study therapy. Two pts discontinued treatment due to pt preference. Median Ki67 at T0 was 14.7%. At T1, 87.5% of pts remained or suppressed Ki67 to <10% and 37.5% suppressed to <2.7%. Ki67 at T1 was similar between pre-and postmenopausal pts despite OFS (Table). The median MRI FTV was 8.4 cc at T0, and 3.4 cc at T3. Median % FTV reduction from T0 to T3 was -47.5%. 2/20 pts (10%) achieved a modified PEPI score of 0. No patients achieved completed pathological response. Of the 16 pts with RCB results, 2 (12.5%) RCB-1, 6 (37.5%) RCB-2, 8 (50%) RCB-3 disease. 14 pts had ctDNA available at T0. 4/14 were ctDNA+ at T0, 2 of whom became ctDNA negative, and 2 remained ctDNA+. 10/14 pts were ctDNA negative at T0, 8 of whom remained negative, 2 became positive at T1 then cleared. All AEs were grade(G) 1 except 1 pt with G2 hot flashes. Most common AEs include hot flashes (85%), constipation (50%), fatigue (50%), and nausea (35%). One pt had G3 hypersensitivity and hypertension, both unrelated to therapy. Conclusions: Neoadjuvant laso demonstrates a favorable AE profile and promising anti-tumor activity in suppressing 3-wk Ki67 and MRI FTV change in pts with HR+ HER2-negative early BC. Ki67 suppression in premenopausal pts was seen in the absence of OFS. Clinical trial information: NCT01042379 . Ki67 expression at pre-treatment, and 3-wk time point. All Patients(n=20) Premenopausal (n=10) Postmenopausal (n=9) Median Ki67 expression Baseline 10.0% 12.5% 10.0% 3-wk 5.1% 3.0% 6.0% Number of pts with Ki67 expression <10% at 3-wk 87.5% 1 87.5% 85.7% Number of pts with Ki67 expression <2.7% at 3-wk 37.5% 50% 28.6% 1 Include the one male pt.

601 Background: EOP is an I-SPY2 neoadjuvant sub-study designed to test the tolerability and impact of novel endocrine-based strategies in stage 2/3 BC pts predicted to have lower benefit from chemotherapy. Amcenestrant (A) is an oral selective estrogen receptor degrader (SERD) with activity in hormone receptor positive (HR+) HER2- metastatic BC. Methods: EOP eligibility included pts screened for the main I-SPY2 trial with HR+ HER2-, MammaPrint (MP) low risk Stage 2/3 BC. Pts with MP High risk tumor signatures were eligible if clinically node-negative (cN-). Pts were stratified by SET index and menopausal status. Pts were randomized to 3 arms: A 200 mg qd (A), A + abemaciclib 150 mg bid (AA), A + letrozole 2.5 mg qd (AL). Premenopausal pts received concurrent ovarian function suppression. Treatment was for 6 mos followed by surgery. Baseline (BL) and 3-wk biopsies were performed. Breast MRIs were conducted at BL (T0), 3 wks (T1), 12 wks (T2), 6 mos (T3). The primary endpoint was feasibility, defined as >75% of pts completing >75% study therapy. Results: Between May 2021 and Aug 2022, 74 pts were randomized: 31 A, 21 AA, 22 AL. Median age 50 years, 54% premenopausal, 38% clinically node-positive (cN+). 41% pts had ductal, 38% lobular, 11% mixed ductal/lobular histology. Mean BL tumor Ki67 (central testing) was 16.9%, 88% MP low, 76% SET index Hi. Pt and tumor characteristics were balanced across the 3 arms. Treatment in all 3 arms was feasible with 95% of pts completing >75% study therapy. Most common AEs include grade 1-2 hot flashes (69%) and fatigue (66%). Grade 3 AEs include neutropenia (2 pts) and diarrhea (1 pt) in AA. Table summarizes key response endpoints, which were similar between pre- and postmenopausal pts. Of 28 cN+ pts, 2 (7%) were pathologically node-negative (pN-). Mean MRI Functional Tumor Volume (cc) change between T0->T1, T1->T2, T2->T3, T0->T3 was -6.06 (-34.2%), -3.55 (-29.2%), -0.829 (-20.1%), -11.3 (-68.4%), respectively, similar across arms (p=0.396).ctDNA was detected in 10/59 (17%) pts at T0. ctDNA became undetectable in 6 pts, decreased in 4 pts, and went from ctDNA undetectable at baseline to detectable at T3 in 2 pts. Conclusions: Six months of neoadjuvant endocrine therapy (NET) with the oral SERD amcenestrant is feasible, well-tolerated, and demonstrates anti-proliferative and anti-tumor activity in pre- and postmenopausal pts. NET provides a rich platform for biomarker discovery and investigating response to endocrine therapy. Clinical trial information: NCT01042379 . [Table: see text]

e12641 Background: Many promising agents or combinations regimens relevant to breast cancer lack sufficient clinical information for use in the neoadjuvant setting. To enable acceleration of drug development by reducing time and cost of clinical trial planning and conduct, the Phase I initiative PRE-ISPY Program was created. Methods: The PRE-ISPY Program is built within the I-SPY network, with the overall aim to streamline the regulatory pathway and the processes of trial design, contracting, activation, enrollment, execution, data gathering and analysis, as well as reporting of new therapeutic agents or combinations of relevance to breast cancer. Results: The PRE-ISPY trial is an open-label platform phase IB study designed to evaluate compelling single agent or combination regimens with the overall goal of moving promising drug regimens into I-SPY2 Trial and/or into other oncology-based trials in a timely manner. Graduation of a PRE-ISPY regimen to I-SPY2 is not mandatory. The primary objectives in each study Arm are to determine safety and to obtain preliminary efficacy data of the new regimen in patients with metastatic cancer, including a cohort of breast cancer patients. Each Arm may contain a Part 1 (dose finding) and a Part 2 (dose expansion). The new treatment can be tested also in patients with other solid malignancies than breast cancer, in which the treatment may be applicable, as specified in the design of the Arm. A breast cancer specific cohort is required in Part 2. Candidate treatment regimens are selected with advice from the I-SPY2 Agent Selection Working Group. The PRE-ISPY/Phase IB trial has multiple ongoing drug regimen Arms subsequently added as new protocol appendices through amendments to a Master protocol. There is no randomization; participants are enrolled, and treatment selected according to the relevance of therapy to their disease. Prospective companion biomarkers are evaluated. The current arms under study are PRE1: ALX-148 combined with trastuzumab deruxtecan; PRE2: tucatinib combined with zanidatamab; and PRE3: vidutolimod combined with cemiplimab. Selected agents or therapeutic combinations are tested through this protocol in the I-SPY Network Centers that participate in the PRE-ISPY Program. Toxicities are graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE). Clinical responses are evaluated based on RECIST v1.1 criteria. Conclusions: Once safety is established, promising regimens can be rapidly transitioned to I-SPY 2.2 or other phase 2/3 trials. The first patient was enrolled on 2/1/2023. Clinical trial information: NCT05868226 .