GLP-1 Drugs Linked to Lower Cancer Progression and Reduced Breast Cancer Incidence — Clinical Studies at ASCO 2026
The potential paradigm shift of GLP-1 receptor agonists into oncology and cancer prevention has been significantly strengthened by a major new study from Penn Medicine. Presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting (Abstract 10506) and published in JCO Oncology Practice on June 2, 2026, the retrospective cohort study of 111,646 women revealed that those taking GLP-1 medications were approximately 30% less likely to develop breast cancer than those who did not.
The researchers, led by Dr. Elizabeth McDonald at Penn’s Abramson Cancer Center, analyzed electronic health records (EHR) of women ages 45 to 80 with a BMI of 25 or above who had breast imaging between January 2022 and June 2025. Out of the full cohort, 15,264 women (13.7%) had documented GLP-1 prescriptions.
To limit confounding factors, the researchers compared the GLP-1 cohort to a smaller, matched cohort of 30,528 women, pairing each GLP-1 patient one-to-one with a control of similar age, race, ethnicity, BMI, breast density, and diabetes status. The reduced breast cancer incidence was consistent across both analyses:
- Full Cohort Analysis: 35.1% lower odds of developing breast cancer.
- Matched Cohort Analysis: 30.5% lower odds of developing breast cancer.
Clinical Mechanisms and Future Trials
While observational, the study adds heavy clinical weight to the theory that GLP-1s can inhibit tumor development. Researchers hypothesize that GLP-1s achieve this through multiple pathways:
- Weight Management: Obesity, particularly post-menopause, is a major risk factor for breast cancer.
- Anti-inflammatory Effects: Low-grade systemic inflammation is linked to breast cancer development. GLP-1s are known to reduce systemic inflammation.
- Metabolic and Epigenetic Effects: GLP-1s may directly influence cellular pathways that inhibit tumor growth.
Because current breast cancer prevention methods (such as prophylactic mastectomy or tamoxifen) are highly invasive or carry significant side effects, the high tolerability and widespread use of GLP-1s make them an attractive candidate for preventative oncology. To establish prospective evidence, McDonald and collaborators are actively working to launch a multi-site clinical trial testing whether GLP-1 medications can lower breast cancer incidence in high-risk women, including those with a history of breast cancer.