Abstract PS1-08-28: The use of oral selective estrogen receptor degraders (SERDs) by community-based general medical oncologists (GMOs) in ER-positive (ER+), HER2-negative (HER2-neg) metastatic breast cancer (mBC): A clinician survey of practice patterns and practical challenges

Abstract Background: The rapid pace of cancer research has created a challenging environment in which GMOs are constantly contending with the introduction of multiple novel agents and regimens often indicated for identical or overlapping patient populations. The 1/2023 approval of elacestrant (E) for patients with mBC and an ESR1 mutation (ESR1mut) whose disease progresses on endocrine therapy (ET) introduced new treatment considerations into a clinical situation which already had multiple approved therapeutic options. Since that time, several additional phase III reports — including 2 potentially practice-changing trials with novel SERD-based strategies (EMBER-3 and SERENA-6) — have added complexity to this space. This initiative sought to better understand GMOs’ familiarity with relevant research and their current and potential use of oral SERDs. Methods: In 9/2025, 50 US-based GMOs completed a case-based survey on the management of ER+ HER2-neg ESR1mut mBC. For each case, clinical factors (age, site/extent of metastases, symptom burden, duration of benefit with first-line treatment, PIK3CA mutations) were varied. The survey also asked GMOs to rate their level of familiarity with and interest in learning more about 12 phase III trials applicable to the management of patients with ER+ HER2-neg mBC. A modest honorarium was offered. Results: In general, GMOs self-reported familiarity with the 12 trials, with a mean overall rating of 3.7 out of 5. They were also very interested in learning more about these studies (mean rating 4.5). In terms of selection of therapy, for a 65-year-old patient with ESR1mut disease, progression 2.5 years after starting first-line CDK4/6 inhibitor (CDKi)/aromatase inhibitor (AI) and minimally symptomatic bone-only mets, 84% of GMOs recommend E. For the same patient with symptomatic visceral mets, 62% would deploy the SERD. For the same patient but with a coexisting PIK3CA mutation, E was preferred by 36% of GMOs in cases with bone mets and by 30% for symptomatic visceral disease. Other factors, including age (80 y) and shorter duration on CDKi/AI (10 mo), did not substantially affect treatment preferences across various situations. In terms of actual experience, GMOs reported using E a median of 4 times. Regarding select other oral SERDs (imlunestrant, camizestrant, giredestrant), 46% of GMOs believe data are not sufficient to determine comparative efficacy. However, 68% consider imlunestrant clinically equivalent whenever E is currently employed, and 72% would consider using it with abemaciclib in select situations. A majority (68%) of GMOs currently would utilize serial monitoring for ESR1mut during first-line treatment and early switching to a SERD (camizestrant) for patients with “molecular progression” ahead of overt clinical progression, as in SERENA-6. Conclusions: While GMOs are generally familiar with the key datasets, they are also highly motivated to learn more. GMOs have rapidly incorporated E into the management of progressive ER+ HER2-neg ESR1mut mBC. Similarities and differences in practice patterns were observed between GMOs and breast cancer research leaders (data available separately) for a number of clinical situations surveyed. In terms of novel SERDs, many GMOs consider the newly approved imlunestrant equivalent to E and would consider its use with abemaciclib in certain circumstances. Many GMOs would use camizestrant for patients found to have an ESR1mut without clinical disease progression, a perspective not shared by the majority of research leaders. This and other differences should be further studied to better understand what is driving the thoughts and recommendations of these different groups of clinicians. Citation Format: K. H. Pang, K. A. Ziel, D. Paley, S. A. Wander, M. R. Lloyd, N. Love. The use of oral selective estrogen receptor degraders (SERDs) by community-based general medical oncologists (GMOs) in ER-positive (ER+), HER2-negative (HER2-neg) metastatic breast cancer (mBC): A clinician survey of practice patterns and practical challenges [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-08-28.