Abstract Introduction: Estrogen plays a critical role in regulating metabolism, body composition and glucose homeostasis. Its decline after menopause increases the risk of metabolic disorders, including type 2 diabetes BC stage 0 (n=1); stage 1 (n =18); stage 2 (n =3); stage 3 (n =1); stage 4 (n =1). One pt had HR+/HER2+ BC; remainder were HER2-negative. All were postmenopausal: 2 were on a GNRH agonist and 5 had prior surgical menopause. ET at weight loss medication initiation: anastrozole (n=17); exemestane (n=3), letrozole (n=2), fulvestrant (n=1); tamoxifen (n=1). Median time on endocrine therapy when starting weight loss medications: 41.5 mo (range 5-107). Common comorbidities: pre-diabetes (29.2%), type II diabetes (16.7%), and hyperlipidemia (70.8%). 8.3% had prior bariatric surgery. Most pts (83.3%,n=20) were prescribed GLP-1 RAs and 16.7% (n=4) phentermine. The GLP-1s used were Zepbound (n=10); Mounjaro (n=5); Wegovy (n=4); Ozempic (n=2); Saxenda (n=2); Victoza (n=1); some pts switched agents during treatment. Median initial weight at time of starting weight loss medications was 192.7 lbs (range 153.9-273). All patients had a baseline and 3 mo follow-up visit, with a mean weight loss of 18.8 lbs between timepoints (p0.001). At 6 mo, 23 patients had available data, showing a mean reduction of 30.9 lbs (p0.001) from baseline. At nine and twelve mo, follow-up data were available for 50% of patients (n=12), with mean weight losses of 39.6 lbs (p=0.033) and 37.9 lbs (p=0.004), respectively. Among the 8 patients with complete data, repeated measures analysis demonstrated a significant weight reduction from an average of 211.7 lbs to 178.9 lbs (p0.001). No new safety concerns were identified. Conclusion: The use of GLP-1 RAs or phentermine in this cohort of patients with HR+ BC on ET was associated with meaningful weight loss, most notably within the first nine months, with weight plateauing thereafter. The degree of weight loss observed was comparable to outcomes reported in the general population using these medications. Limitations include a small sample size and grouping of all weight loss agents together. Updated data with a larger sample size and body composition analysis, will be presented. Prospective studies are warranted to further assess long-term efficacy in this pt population. Citation Format: T. Adamson, N. E. Gharaibeh, R. Shaw, C. D. Morrissey, S. Kapoor, A. Podolski, E. Teplinsky. Evaluating weight loss outcomes in patients with hormone receptor-positive breast cancer on endocrine therapy receiving concurrent weight loss medications 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 PD8-02.
Adamson et al. (Tue,) studied this question.