Real-world treatment patterns and mortality associated with GLP1-RAs in breast cancer patients.

629 Background: GLP1 Receptor Agonists (GLP1) are widely used for type 2 diabetes (DM2) and obesity in adults. However, data on modern utilization and associated health outcomes, including all-cause mortality, in breast cancer (BC) patients is limited. We evaluated these endpoints in a BC population from a large US national healthcare database. Methods: Using Truven MarketScan, a commercial insurance claims database which includes over 270 million patients, we extracted eligible invasive BC patients diagnosed between 2014 and 2023 who were ≥ 18 years old, completed definitive BC surgery (index date), received GLP1 for at least 3 continuous months, and had available mortality data. Overall survival (OS) was defined as the time from BC surgery to death from any cause; patients alive at the time of analysis or lost to follow-up were censored at last contact date. Propensity score matching (1:1 ratio) was used to match patients who received GLP1 with those who did not, based on clinical prognostic factors (age; sex; deyo comorbidity index (CI); receipt of immunotherapy, chemotherapy, adjuvant endocrine therapy; DM2; weight category; stroke; myocardial infarction (MI)/coronary artery disease (CAD); heart failure); Kaplan-Meier estimates and log-rank tests were used to compare OS between groups and hazard ratios (HR) were estimated using multivariable Cox proportional hazards models. Results: In 137,493 BC patients, 7,249 (5.3%) received a GLP1 and over half (n=4,019; 55.4%) initiated it after BC surgery. The median follow up time in GLP1 users was 32 (IQR 15-57) months. In GLP1 users the median age was 59 (IQR 53-64) years; 5,860 (80.8%) had DM2 and 1,825 (25.2%) had a CI ≥3; in those with weight data available (n=4,687), 4,609 (98.3%) were in the overweight or obese category. A total of 3,828 (52.8%) received GLP1 concurrent with anti-cancer systemic therapy (chemotherapy, immunotherapy, or adjuvant endocrine therapy). The median duration of GLP1 use was 2.1 (IQR 0.8-6.1) years. GLP1 use increased over time (3.2% in 2014, 5.2% in 2018, 7.2% in 2023). Semaglutide was the most common agent prescribed across all years (35.8%) and exhibited the greatest annual increase in use after 2018. In the propensity score matched cohort, OS was significantly higher in GLP1 users vs non-users (n=7,248 per group): 5 year OS 95.8% GLP1 vs. 89.5% non-users (adjusted HR 0.41, 95% CI: 0.34-0.49, p