GLP-1 Drugs Linked to Lower Cancer Risk in Observational Studies, but Causation Unproven

Analyses of medical records from more than 10,000 patients with early-stage cancer showed GLP-1 drugs reduced risk in six of seven cancer types examined. Four cancers reached statistical significance: breast, liver, colorectal, and non-small cell lung cancer. Kidney and prostate cancer risks declined somewhat, while pancreatic cancer rates showed the smallest change.

3 percent of patients not taking GLP-1 drugs, compared with 10 percent among those who did. A separate analysis matched mammogram images to prescription data and found women aged 45 to 80 who took GLP-1 drugs were 30 percent less likely to develop breast cancer. The findings were presented at the American Society of Clinical Oncology meeting held in May 2026.

The society highlighted four studies, some published in its Journal of Clinical Oncology. GLP-1 drugs were originally developed as diabetes treatments and later shown to aid weight loss, heart disease, and sleep apnea. Dr.

Julie Gralow, chief medical officer of ASCO, said the data remain correlative because the retrospective databases did not capture comorbidities, exercise, or eating habits. She noted the results align with existing knowledge that obesity drives about a dozen cancers and that healthy lifestyles affect both illness and recovery.

Elizabeth McDonald, a radiologist at the University of Pennsylvania and co-author of the breast-cancer study, said the protective effect exceeded what weight loss alone would explain.

She said GLP-1 medicines may reduce inflammation, a known driver of cancer, by acting on metabolic pathways beyond hunger and digestion. Oncologist Coral Omene at Rutgers Cancer Institute plans to follow 40 breast-cancer patients beginning tirzepatide, sold as Mounjaro and Zepbound.

She will measure blood samples, track cancer markers, and biopsy abdominal fat cells every six months to observe changes in hormones and inflammation.

"And as we're treating them, we are going to trace and see how the immune cells are behaving," Omene said. The trial aims to clarify how GLP-1 drugs might be used against cancer.