GLP-1 drugs show promising signs of slowing cancer progression

Quartet of observational studies points to tumor-suppressing effects of Ozempic and Mounjaro, though randomized trials remain absent

The blockbuster class of weight-loss and diabetes medicines known as GLP-1 drugs may carry an unexpected benefit for cancer patients, according to four new studies suggesting the treatments are associated with slower tumor progression and improved survival rates.

Research presented ahead of the American Society of Clinical Oncology's annual conference points to meaningful reductions in cancer advancement among patients taking semaglutide — sold by Novo Nordisk (NVO) under the brand names Ozempic and Wegovy — and tirzepatide, marketed by Eli Lilly (LLY) as Mounjaro and Zepbound.

A study from the Cleveland Clinic Cancer Institute, tracking more than 10,000 patients with early-stage cancers who were prescribed GLP-1 drugs following diagnosis, found substantially lower rates of disease progression compared with patients on alternative diabetes medications. In lung cancer, the rate of progression to advanced disease was roughly halved — 10 per cent among GLP-1 users against 22 per cent in the comparison group. Breast cancer patients showed a near-identical gap, with rates of 10 per cent versus 20 per cent. Colorectal and liver cancers also produced statistically significant reductions.

Separate research from the University of Texas MD Anderson Cancer Center, drawing on records from more than 137,000 breast cancer patients, found that more than 95 per cent of GLP-1 users were alive five years after diagnosis, compared with 89.5 per cent for non-users. A University of Pennsylvania analysis of nearly 95,000 women undergoing breast imaging found that those who had taken a GLP-1 drug were approximately 25 per cent less likely to receive a breast cancer diagnosis, after adjusting for age, weight and other risk factors.

"It's really provocative that they showed, in several cancers, that people who took these drugs seem to have a lower risk of their cancer returning," said Dr Jennifer Ligibel, a breast oncologist at the Dana-Farber Cancer Institute, who was not involved in any of the studies.

The findings, if confirmed, would extend further still a therapeutic profile that has already upended global pharmaceuticals. Beyond glycaemic control and weight reduction, GLP-1 drugs are approved for cardiovascular risk reduction and are under investigation for applications ranging from sleep apnoea to addictive behavior. The commercial implications have been transformative: Novo Nordisk and Eli Lilly have become two of the highest-valued pharmaceutical companies in the world on the strength of GLP-1 demand, even as governments and insurers struggle to contain costs.

Neither company is currently conducting trials examining the drugs' effects on cancer.

Scientists remain uncertain about the mechanism behind the observed associations. One hypothesis holds that GLP-1s reduce cancer risk indirectly, through weight loss and improved metabolic health — both of which are independently associated with lower cancer incidence. A more direct explanation points to the presence of GLP-1 receptors on the surface of certain tumor cells, raising the possibility of a pharmacological effect on cancer biology itself.

Researchers and clinicians urged caution, however. All four studies are observational in design, relying on retrospective analysis of insurance claims and hospital databases rather than controlled experimentation. Patients prescribed GLP-1 drugs tend to have greater access to healthcare and more consistent clinical follow-up — advantages that may independently improve outcomes and confound the results.

"We're seeing a signal across databases which is certainly interesting because all of these studies have slightly different designs," said Dr Jasmine Sukumar, a breast oncologist at MD Anderson and co-author of the survival study.

Randomized controlled trials, which allocate patients to treatments by chance and more rigorous control for confounding variables including income, baseline health and healthcare access, remain the standard by which causality is established in clinical medicine. None are currently under way for this indication.

Despite those caveats, the breadth of the data — spanning hundreds of thousands of patients across multiple cancer types and institutional databases — has drawn attention from oncologists who might otherwise have been skeptical of industry-adjacent findings.

"It's hard to ignore the numbers," said Dr Jaroslaw Maciejewski, vice-chair at the Cleveland Clinic Cancer Institute.