Glucagon-like peptide-1 (GLP-1) agonist use and weight change among patients with breast cancer.

10607 Background: Elevated body mass index (BMI) and post-diagnosis weight gain increase the risk of breast cancer recurrence and all-cause mortality. Chemotherapy and endocrine therapy can worsen metabolic dysfunction and are associated with weight gain. GLP-1 agonists mimic the action of endogenous GLP-1 and stimulate insulin secretion, delay gastric emptying, and promote satiety. In addition to diabetes treatment, several of these agents induce substantial (8-15%) weight loss and are indicated for obesity weight management. The efficacy of GLP-1 agonists during or after breast cancer treatment is unclear. Methods: Patients with breast cancer and prescribed a GLP-1 agonist from 2015-2023 with follow-up weight data (pre- and on/post-GLP-1 agonist) were included in this retrospective cohort study. A linear mixed effects model with a random intercept for baseline patient weight was used to assess mean weight change at each available follow-up timepoint. Relative weight change from baseline to approximately 12 months after GLP-1 agonist initiation was also computed and a multivariable linear regression was used to assess the association of baseline covariates with relative weight change. Results: 75 patients were included; median age was 52 (range 27-74), 4 (5%) had carcinoma in situ, 64 (85%) had stage I – III, and 4 (5%) had stage IV breast cancer. 62 (83%) had hormone receptor-positive tumors; 14 (19%) had HER2-positive and 8 (11%) had triple negative tumors. 40 (53%) received an aromatase inhibitor concurrently with GLP-1 agonist whereas 3 (4%) received tamoxifen concurrently. Chemotherapy was administered to 56 (75%), and 44 (59%) received radiation. 59 (79%) had a diagnosis of diabetes. Median time from breast cancer diagnosis to GLP-1 agonist prescription was 4.3 years (range -4.4 to 29.5). Median weight at breast cancer diagnosis was 85 kg (range 52-163), median BMI was 32 kg/m 2 (range 20-53). Median weight upon GLP-1 agonist initiation was 90 kg (range 58-151) and median BMI was 34 kg/m 2 (range 23-50). Median duration of GLP-1 agonist use was 20 months (range 6-111). At 12 months after GLP-1 agonist initiation, mean relative weight change was -5% (SD 6%). Mean weight change from GLP-1 agonist initiation was -2.8 kg (95% CI -0.9 to -4.7) at 6 months, -4.2 kg (95% CI -2.1 to -6.2) at 12 months, and -6.2 kg (95% CI -3.7 to -8.7) post-GLP-1 agonist treatment. Baseline BMI, concurrent anti-estrogen therapy, duration of GLP-1 agonist therapy, and comorbid diabetes were not associated with relative weight change in multivariate models. Conclusions: The use of GLP-1 agonists in this cohort of patients treated for breast cancer was efficacious and associated with modest (5%) weight loss. Based on this observed activity, prospective trials are warranted.