A striking finding has emerged from research on blockbuster weight-loss medications: women taking GLP-1 drugs like Ozempic and Wegovy show roughly 30 percent lower rates of breast cancer compared to those not using the medications.
The discovery, presented at the 2026 American Society of Clinical Oncology Annual Meeting and published in JCO Oncology Practice, involved analysis of electronic health records from over 111,000 women ages 45 to 80 treated within the Penn Medicine system between January 2022 and June 2025. Among them, about 13.7 percent had prescriptions for GLP-1 drugs while the remainder had no documented exposure.
When researchers compared women on the medications with similar non-users matched by age, race, ethnicity, body mass index, breast density, and diabetes status, those taking GLP-1 drugs showed 30.5 percent lower odds of breast cancer. In the broader analysis of all 111,646 women, the advantage climbed to 35.1 percent.
"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," said Elizabeth McDonald, MD, PhD, a breast radiologist at the University of Pennsylvania's Abramson Cancer Center.
GLP-1 medications, which include semaglutide-based drugs like Ozempic and Wegovy as well as tirzepatide products such as Mounjaro and Zepbound, were originally developed to treat type 2 diabetes. They work by mimicking glucagon-like peptide-1, a naturally occurring hormone that regulates appetite and blood sugar. What started as diabetes therapy has exploded into one of America's most popular weight-loss treatments.
The link between GLP-1 use and lower cancer risk intrigues researchers because these drugs were never designed with cancer prevention in mind. Yet they influence multiple biological pathways implicated in tumor development. McDonald and colleagues are now working to launch a multisite clinical trial specifically examining whether GLP-1 medications can reduce breast cancer incidence in high-risk women.
Weight loss itself plays a role. Excess weight, particularly after menopause, is a well-established risk factor for breast cancer. GLP-1 drugs are remarkably effective at promoting weight reduction, so some benefit likely stems from that effect alone. But scientists suspect additional mechanisms are at work.
Chronic low-grade inflammation has long been suspected as a contributor to breast cancer development. GLP-1 medications reduce inflammation through several biological pathways. They also influence metabolic processes and can affect epigenetic activity, which regulates how genes are expressed. These combined effects may help suppress breast cancer formation.
Current prevention options remain limited. Routine screening through mammography or MRI catches existing cases, while some high-risk individuals with genetic mutations opt for preventive surgery. Tamoxifen can substantially reduce breast cancer risk in eligible patients but many refuse it due to side effect concerns.
GLP-1 drugs present an intriguing alternative. Millions of Americans already use them, making them far more appealing as a potential prevention tool than novel compounds that would require extensive development and approval.
The researchers acknowledged several study limitations. They could not distinguish between individual medications like Ozempic versus Mounjaro, nor did they account for how long patients took the drugs, inherited genetic risk factors, cancer stage, or tumor subtypes. Additional analyses are underway to examine these variables.
McDonald emphasized the broader goal driving this work. "Ultimately, we want to find better options to prevent breast cancer," she said. "It's been encouraging to see the survival rates for breast cancer improve over recent decades, and we'd love to see the same gains in prevention."
Author Jessica Williams: "This finding could reshape how we think about GLP-1 drugs, turning medications already reshaping the weight-loss landscape into potential cancer prevention tools, though the research still needs rigorous clinical trials before doctors start prescribing them for that purpose."
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