JCO Oncol Pract
ASCO 2026: GLP-1s tied to 30% lower odds of breast cancer
Clinical takeaway: GLP-1 use was linked to fewer breast cancer diagnoses in overweight and obese women, adding to early signals around obesity-related cancers.
Excess weight is one of the few modifiable risk factors for breast cancer. Other effective ways to prevent the disease are few, and those that exist carry significant risks or side effects. GLP-1 drugs, now used by millions for weight loss, raise an obvious question: might they also lower breast cancer risk? This study is among the first to examine that question in a population made up entirely of women eligible for screening.
GLP-1 users were diagnosed with breast cancer about 30% less often than matched controls. In the matched cohort, 1.62% of users were diagnosed during the study period versus 2.31% of non-users, corresponding to an odds ratio of 0.70.
The absolute difference was small at 0.69 percentage points, or roughly seven fewer cancers per 1,000 women. The unmatched comparison across the full cohort showed a similar direction and a slightly larger gap. The reduction held in both Black and White women when analyzed separately.
The analysis drew on electronic health records from a large academic and community health system covering 111,646 women aged 45 to 80 with a BMI of 25 or above who had breast imaging and a documented outcome between January 2022 and June 2025. To limit confounding, the researchers built a matched cohort of 30,528 women, pairing each GLP-1 user 1:1 with a non-user on age, race, ethnicity, BMI, breast density, and diabetes status.
The study did not account for which GLP-1 drug, dose, or duration of use, and some controls may have obtained the drugs outside the system. The finding aligns with prior observational work, including a 1.1-million-patient analysis and studies of bariatric surgery. The next step is a prospective randomized trial, which the group is working to launch.
"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 professor of Radiology in the University of Pennsylvania Perelman School of Medicine and a practicing breast radiologist at Penn’s Abramson Cancer Center.
Source: McDonald ES. JCO Oncol Pract. 2026 Jun 2. GLP-1 agonists are associated with a significant reduction in breast cancer incidence in women