A large observational study presented at the 2026 American Society of Clinical Oncology (ASCO) annual meeting has found that women taking glucagon-like peptide-1 receptor agonists (GLP-1 agonists) — including popular weight-loss drugs like Ozempic and Mounjaro — were roughly 30% less likely to develop breast cancer. The finding held regardless of age, race, ethnicity, body mass index, breast density, or diabetes status.
The research, led by Elizabeth McDonald, professor of radiology at the University of Pennsylvania Perelman School of Medicine and a breast radiologist, analyzed data from more than 110,000 women between the ages of 45 and 80. McDonald noted that these medications were not originally designed for cancer therapy but affect multiple biological pathways linked to tumour development. “GLP-1 medications are intriguing from a cancer research perspective because they weren’t designed for cancer therapy, but they do affect many different targets and pathways associated with cancer development, so we’re eager to study them in this context,” she said.
Mechanisms Beyond Weight Loss
GLP-1 agonists work by mimicking natural gut hormones released after eating, prompting the body to release more insulin, reduce appetite, and maintain lower blood sugar levels. While their primary use has been for type 2 diabetes and obesity, the authors of the study stress that increasing evidence points to additional benefits, including reductions in systemic inflammation — a known factor in the development and progression of breast cancer.
“There is extensive evidence that weight influences breast cancer risk and that lifestyle modification, including weight loss, can reduce this risk,” the researchers wrote. However, they emphasised that the observed risk reduction appeared independent of weight loss itself, suggesting that the drugs’ anti-inflammatory effects may play a key role. Chronic inflammation can create an environment that helps cancer cells grow, survive, or spread more easily.
Breast cancer remains one of the most common malignant tumours among women worldwide. In Europe, it is the leading cause of cancer death among women, with incidence rates varying significantly across the continent — from around 90 per 100,000 in Southern Europe to over 130 per 100,000 in Northern and Western Europe, according to the European Cancer Information System.
Caveats and Next Steps
The study was restricted to women with overweight or obesity, meaning the findings may not apply to women of other body weights. The authors also caution that women taking GLP-1 drugs tend to have more frequent medical check-ups, which could lead to higher cancer detection rates and potentially skew the results. “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.
The researchers are now calling for a randomised trial to evaluate what they describe as a “trifecta of prevention”: cancer, heart disease, and the metabolic changes and symptomatology associated with menopause. Such a trial would be particularly relevant for European health systems, where ageing populations and rising obesity rates are straining public health budgets. The potential for a single intervention to address multiple chronic conditions could have significant implications for healthcare planning across the EU and the wider continent.
Other studies presented at ASCO this year reinforce the trend. A separate Italian study found that women with advanced, hormone receptor-positive breast cancer — the most common subtype — who took GLP-1 drugs lived on average nearly 19 months longer than those who did not. This adds to a growing body of research suggesting that these medications may have broader applications than originally intended.
As Europe grapples with rising rates of obesity and associated cancers, the findings offer a promising avenue for further investigation. However, the authors caution that until randomised trials confirm the results, these drugs should not be prescribed solely for cancer prevention. The study underscores the importance of continued research into the intersection of metabolic health, inflammation, and oncology — a field that could reshape preventive medicine in the coming decade.
