In a large study presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, researchers found that women who used GLP-1 medications were significantly less likely to be diagnosed with breast cancer than women who did not use these drugs. While the findings do not prove that GLP-1 medications prevent breast cancer, they add to growing evidence that these treatments may offer benefits beyond weight management and blood sugar control.
Why This Matters
Breast cancer remains the most commonly diagnosed cancer among women in the United States, aside from skin cancers. Researchers have long known that excess body weight can increase the risk of developing several types of cancer, including postmenopausal breast cancer. As the use of GLP-1 medications continues to rise, scientists are increasingly interested in understanding whether the drugs may also influence cancer risk.
The new study suggests that women taking GLP-1 medications may experience a lower incidence of breast cancer, raising questions about how these drugs affect the body and whether they could one day play a role in cancer prevention strategies.
What the Study Found
Researchers at the University of Pennsylvania analyzed health records from more than 111,000 women between the ages of 45 and 80 who were overweight or obese and underwent breast imaging within the Penn Medicine health system between 2022 and 2025. Among the women included in the analysis, more than 15,000 had been prescribed a GLP-1 medication, while approximately 96,000 had not.
After comparing breast cancer diagnoses between the two groups, investigators found that women using GLP-1 medications had substantially lower odds of developing breast cancer. The association remained significant even after researchers matched participants based on age, body mass index (BMI), race, ethnicity, breast density, and diabetes status. According to the study, GLP-1 users experienced approximately a 30% to 35% reduction in the odds of developing breast cancer compared with non-users.
How Might GLP-1 Medications Influence Cancer Risk?
Researchers do not yet know exactly why GLP-1 use was associated with lower breast cancer incidence, but several possible explanations exist. One is weight loss. Obesity is a recognized risk factor for postmenopausal breast cancer, and many people taking GLP-1 medications experience significant reductions in body weight. Losing excess weight may help lower levels of hormones and inflammatory signals that can contribute to cancer development.
Scientists are also investigating whether GLP-1 medications may have direct biological effects that influence cancer-related pathways. Some studies suggest the drugs may help reduce chronic inflammation and improve metabolic health, both of which have been linked to cancer risk.
Additional research will be needed to determine whether the observed benefit is primarily related to weight loss or if other mechanisms are involved.
What Patients Should Know
Although the findings are encouraging, experts caution that this study cannot prove that GLP-1 medications prevent breast cancer. The research was observational, meaning investigators reviewed existing health records rather than randomly assigning patients to receive treatment. The study also did not examine whether certain GLP-1 medications performed differently from others, whether longer treatment duration influenced risk, or whether the findings varied across breast cancer subtypes. For now, GLP-1 medications are not approved as a strategy for breast cancer prevention. Patients should not start or stop any medication based solely on these results and should discuss treatment decisions with their healthcare team.
Safety Considerations
This study focused on breast cancer incidence and did not report new safety findings related to GLP-1 medications. Like all medications, GLP-1 therapies can cause side effects. The most common include nausea, vomiting, diarrhea, constipation, and abdominal discomfort. Patients considering these medications should review the potential benefits and risks with their healthcare provider.
References:
- McDonald E, et al. Association Between GLP-1 Receptor Agonist Use and Breast Cancer Incidence in Women With Overweight or Obesity. Presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting. Abstract 10506. Published in JCO Oncology Practice, June 2026.
