Abstract 7380: Association of weight loss promoting medications with male breast cancer incidence, tumor grade, and stage: a SEER-Medicare nested case-control study

Abstract Background: Obesity has been associated with an increased incidence of male breast cancer (MBC), including the high-grade and advance-stage of the disease. With the rising use of weight loss-promoting medications (WLPMs), including the use of metformin, there is a growing interest in their potential to positively influence cancer outcomes. Yet, there is a poor understanding about the impact of WLPMs and metformin on the incidence of MBC, stage and grade, presenting a significant gap in research. Methods: We conducted a nested case-control study using the Surveillance, Epidemiology, and End Results (SEER)-Medicare database. The cohort included 2, 444 MBC cases and 12, 068 matched controls (1:5 by birth year and diagnosis date), all of whom had continuous Medicare Part A/B enrollment for at least one year between 2008 and 2019. Pre-diagnostic exposure to WLPMs and metformin was determined through prescription records. Multivariable weighted conditional logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for MBC incidence, advanced-stage cancer (stage 4), and high tumor grade (grade 3). Results: Among MBC cases, 83% were Non-Hispanic White, 34% were >=80 years, 75% had hypertension, 56% had hyperlipidemia, 36% had diabetes and 16% used metformin over 6 months prior to index date. Metformin use was associated with a reduced risk of MBC incidence (OR 0.64, 95% CI 0.54-0.74), and high tumor grade (OR 0.57, 95% CI 0.41-0.78). However, it was linked to an increased likelihood of advanced-stage cancer (OR 1.79, 95% CI 1.26-2.56). WLPMs did not significantly affect the incidence, tumor grade and stage of MBC. Conclusion: Our findings suggest that metformin may reduce the risk of MBC incidence but could be associated with advanced-stage disease at diagnosis. Further research is needed to explore the effects of WLPMs on MBC outcomes. Citation Format: Aniruddha B. Rathod, Biai Dominique Elmir Digbeu, Jenil R. Patel, David S. Lopez. Association of weight loss promoting medications with male breast cancer incidence, tumor grade, and stage: a SEER-Medicare nested case-control study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 7380.