GLP-1 Drugs Linked to 30% Drop in Breast Cancer Risk in 111,000-Woman Study

Women with a body mass index of 25 or higher who took GLP-1 receptor agonist medications were about 30% less likely to be diagnosed with breast cancer than comparable women who didn't take them, according to a large retrospective study published June 2 in JCO Oncology Practice and presented at the 2026 American Society of Clinical Oncology Annual Meeting in Chicago.

The study, managed by the American College of Radiology and led by Dr. Elizabeth McDonald, a professor of radiology at the University of Pennsylvania Perelman School of Medicine, drew on health records from more than 111,000 women between the ages of 45 and 80. Of those women, nearly 14% had been prescribed a GLP-1 drug. The researchers then matched GLP-1 users against non-users and found that, in the matched cohort, 1.62% of users were diagnosed with breast cancer during the study period versus 2.31% of non-users, an odds ratio of 0.70. In absolute terms that's roughly seven fewer cancers per 1,000 women.

The reduction held when researchers looked at Black women and white women separately, which matters because breast cancer incidence and outcomes differ by race. The unmatched comparison across the full cohort pointed in the same direction and showed a slightly larger gap, with some analyses reaching up to 35% lower risk.

Those numbers are striking, but McDonald was careful about what they mean. In a statement reported by U.S. News and World Report, she said the study "does not definitively confirm an association" and framed the findings as evidence that GLP-1 drugs are "worth investigating as potential cancer prevention tools." That's the right read. Retrospective analyses can't rule out confounding. Women prescribed GLP-1s may differ from non-users in ways the data don't fully capture, including how often they see a doctor, which affects screening rates and therefore detection.

The study population is worth naming precisely: women aged 45 to 80 with a BMI of 25 or higher, many recruited through the TMIST breast cancer screening trial, which itself enrolled about 21% African American participants in its U.S. cohort. That's a more diverse population than many drug studies, and it strengthens the signal that the finding isn't limited to one demographic group.

GLP-1 drugs, which include semaglutide (sold as Ozempic and Wegovy) and tirzepatide (Mounjaro and Zepbound), were originally developed for type 2 diabetes. They reduce appetite and slow gastric emptying by mimicking the GLP-1 hormone. Cardiovascular outcome data came next, then an approval for obstructive sleep apnea. Evidence has been building around kidney disease, fatty liver disease, and alcohol dependence as well. A 2024 study in Nature Medicine documented lower rates of multiple obesity-associated cancers in GLP-1 users. The ASCO 2026 data adds breast cancer specifically to that list.

The mechanism behind any cancer benefit isn't settled. Weight loss itself reduces breast cancer risk, particularly for postmenopausal women, because adipose tissue produces estrogen. But some researchers suspect GLP-1 receptors may have direct effects on tumor biology independent of weight, a question a prospective trial could begin to untangle.

The American College of Radiology is already calling for funding to run exactly that trial. Plans reported by Oncology Nursing News indicate a multisite clinical trial is in development, targeting high-risk women including those with a prior breast cancer history. Until that data exists, oncologists and primary care clinicians aren't likely to prescribe GLP-1s for cancer prevention, nor should they. But for the millions of women already on these drugs for diabetes or obesity, this is one more signal that the risk-benefit math may lean further in their favor than the original approvals reflected.

Sources cited:
- JCO Oncology Practice / ACR press release (https://www.acr.org/News-and-Publications/Media-Center/2026/acr-study-suggests-drug-lowers-breast-cancer-risk)
- Oncology Nursing News (https://www.oncnursingnews.com/view/glp-1-use-linked-to-30-reduced-breast-cancer-risk-in-large-cohort-study)
- Epocrates / ASCO 2026 summary (https://www.epocrates.com/online/article/asco-2026-glp-1s-tied-to-30-lower-odds-of-breast-cancer)
- U.S. News and World Report / HealthDay (https://www.usnews.com/news/health-news/articles/2026-06-03/glp-1-drugs-like-ozempic-may-lower-breast-cancer-risk-by-about-30)
- WHYY (https://whyy.org/articles/lower-breast-cancer-risk-glp-1-use/)