A Timely Question in Cancer Prevention

Excess body weight is a modifiable risk factor for breast cancer, while glucagon-like peptide-1 receptor agonists (GLP-1 RAs) promote weight loss and improve metabolic health. Their expanding use raises an important prevention question: could exposure to these agents be associated with a lower incidence of breast cancer? A large retrospective study presented at the 2026 ASCO Annual Meeting examined this association among women undergoing breast imaging at a major academic center.

Study Design and Cohort Development

Investigators used electronic health records from January 1, 2022, through June 30, 2025, to identify women who underwent breast imaging. The analysis focused on women aged 40 to 80 years with a body mass index of at least 25 and a documented imaging outcome. GLP-1 RA exposure was defined by a first prescription before the imaging examination date, and the primary outcome was breast cancer detection.

The slide presentation described a stepwise cohort derivation from 217,624 unique women to 111,646 eligible women, with a median age of 61 years. To reduce measured differences between exposed and unexposed patients, investigators performed one-to-one propensity-score matching based on age, race, ethnicity, highest body mass index, breast density, and type 2 diabetes. Covariate-balance assessment showed improved balance after matching.

Lower Breast Cancer Incidence in Matched and Unmatched Analyses

In the full unmatched cohort, 15,264 women had prior GLP-1 RA exposure and 96,382 did not. Breast cancer was detected in 1.62% of exposed women and 2.6% of unexposed women. In adjusted logistic regression, prior GLP-1 RA exposure was associated with lower breast cancer incidence, with an odds ratio of 0.649.

The matched analysis included approximately 30,000 women, evenly divided between exposed and unexposed groups. Breast cancer was detected in 1.62% of women with prior GLP-1 RA exposure and 2.31% of women without exposure. The corresponding odds ratio was 0.695, and the absolute risk reduction was 0.69 percentage points, with a 95% confidence interval of 0.38 to 1.01 percentage points. Findings were directionally consistent across both analytic approaches.

How the Findings Should Be Interpreted

The presentation emphasized that these data are hypothesis generating and do not establish causality. Even after propensity-score matching, unmeasured differences may remain between women who did and did not receive GLP-1 RAs. The analysis established exposure from prescription records, but the materials did not specify treatment adherence, duration, dose, weight change after treatment, or the biologic subtype of detected cancers.

Several mechanisms could plausibly contribute to the association, including weight reduction, improved insulin resistance and metabolic dysfunction, reduced systemic inflammation, and direct effects on cellular metabolism or tumor biology. However, this study was not designed to determine which mechanism, if any, explained the observed difference.

Practice Takeaway

In this large observational cohort of women undergoing breast imaging, prior GLP-1 RA exposure was associated with a lower incidence of breast cancer in both unmatched and propensity-matched analyses. The consistency of the signal supports further study, but the results remain associative and are not sufficient to recommend GLP-1 RAs as breast cancer prevention drugs.

References

1. McDonald ES, Gillis LB, Gabriel PE, et al. Association of GLP-1 agonists with breast cancer incidence in women. Slide presentation. Presented at: 2026 American Society of Clinical Oncology Annual Meeting. Abstract 10506.
2. McDonald ES, Gillis L, Gabriel P, et al. Association of GLP-1 agonists with breast cancer incidence in women. J Clin Oncol. 2026;44(suppl). Abstract 10506. doi:10.1200/JCO.2026.44.16_suppl.10506