Abstract Background Obesity and diabetes are common comorbid conditions found in patients with breast cancer and these conditions have been linked to risk of recurrence and early mortality. GLP-1 receptor agonists have changed the paradigm for weight loss and diabetes management, but the prevalence, timing of initiation and duration of use among women with a breast cancer history is not well described. Further, efficacy for weight loss may vary by diabetes status and treatment factors such as the use of endocrine therapy. Methods: To address these knowledge gaps, our retrospective analysis utilized tumor registry and electronic health record data to identify all patients with a breast cancer history who initiated semaglutide (and/or tirzepatide) therapy from 2020-2025 at Kaiser Permanente Northern California, a large integrated community oncology network in the US. Results: 1,753 patients with breast cancer history initiated semaglutide in the years 2020-2025. The majority of patients were diagnosed with stage 0 or I/II breast cancer (344 19.6% and 1,146 65.4%, respectively) and 1,456 (83.1%) of patients had estrogen receptor (ER) positive breast cancer. 1,245 (71.0%) had diabetes at initiation. The average age at initiation was 63.5 years, with a median (IQR) time from breast cancer diagnosis to semaglutide initiation of 7 (3-13) years. 1,296 (73.9%) had ever used endocrine therapy, with 685 (39.1%) on active endocrine therapy at semaglutide initiation. Most patients had 1 semaglutide dispense (1,718 98.1%), but more than one third continued use beyond 1 year. Mean (SD) BMI at semaglutide initiation was similar among the non-diabetic (37.4 7.2 kg-m2) vs. the diabetic (36.4 7.5 kg/m2) group, with a mean maximum achieved weight loss of 11.2% and 8.6%, respectively. When stratified by history of endocrine therapy, rates of continuation at one year and achieved weight loss were similar between groups. Conclusion: In patients with breast cancer, semaglutide therapy was most commonly initiated for diabetes and was associated with weight loss, even among those receiving endocrine therapy. However, the maximum observed weight loss was less than that observed in clinical trials in non-cancer populations. Long-term adherence was limited, with only one-third continuing use beyond one year. Our study highlights the role of real-world data in understanding the effects of GLP1- receptor agonist drugs in patients with breast cancer. Future studies should investigate whether the use of these agents reduces risk of recurrence and mortality. Citation Format: J. Song, R. Liu, S. K. Zhong, P. Mishra, S. Zhu, E. Feliciano. Characteristics and weight loss outcomes in patients with breast cancer prescribed semaglutide 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 PS1-05-22.
Song et al. (2026) studied this question.