A study of over 110,000 women presented at the 2026 American Society of Clinical Oncology Annual Meeting has found that GLP-1 medications—commonly used for weight loss and diabetes management—were linked to roughly 30% lower breast cancer incidence, offering a striking new clue in the hunt for non-invasive cancer prevention tools.
The research, conducted by Dr. Elizabeth McDonald, a breast radiologist and professor of Radiology at the University of Pennsylvania Perelman School of Medicine, analyzed health records from women ages 45 to 80 with a body mass index of 25 or above between January 2022 and June 2025. Of the 111,646 women in the full cohort, 15,264 (13.7%) had documented GLP-1 prescriptions, while 96,382 did not. The researchers found that women taking GLP-1 medications had 35.1% lower odds of developing breast cancer in the full analysis and 30.5% lower odds in a matched cohort of 30,528 women carefully controlled for age, race, ethnicity, BMI, breast density, and diabetes status.
What makes this finding particularly significant is how desperately the field needs new prevention strategies. Beyond regular mammography and MRI screening, medical options to reduce breast cancer risk remain limited—prophylactic mastectomy is offered to those with high-risk genetic mutations, and tamoxifen carries serious side effects. Most women have few evidence-based options beyond weight management and lifestyle modifications. That's why McDonald and her team are investigating whether medications never originally designed to prevent cancer might do exactly that.
GLP-1 drugs mimic glucagon-like peptide-1, a natural hormone that regulates blood sugar and appetite. Originally developed to treat type 2 diabetes, they've gained enormous popularity for weight management in recent years. But their impact on the body extends far beyond appetite suppression. These medications reduce systemic inflammation through multiple pathways and produce metabolic and epigenetic effects that could inhibit tumor growth—all potential cancer-fighting mechanisms that deserve closer study.
"While our study was observational and does not definitively confirm an association between GLP-1 medications and reduced breast cancer incidence, it does add to the growing body of evidence suggesting that it's worth investigating these weight-loss drugs as potential cancer prevention tools," McDonald said in a statement accompanying the research, published in JCO Oncology Practice.
The research has important limitations. The study did not account for which specific GLP-1 medications women took, how long they used them, their genetic risk factors, or cancer stage or type at diagnosis. Those variables will be examined in further analyses already underway. Yet the consistency of the finding across two different analytical approaches—the full cohort and the carefully matched subset—suggests the association is robust enough to justify the next step.
McDonald and her collaborators are now actively working to establish a multisite clinical trial to test whether GLP-1 medications can actually reduce breast cancer incidence in high-risk women, including those with a personal history of the disease. Such a prospective trial would provide the kind of rigorous evidence that currently doesn't exist for this drug class and cancer prevention. Until then, this observational study stands as a reminder that sometimes the most promising therapeutic discoveries come from unexpected places—and that the most effective cancer prevention tool might be one we've already begun to use for something else entirely.