A new study suggests that the anti-obesity drug tirzepatide may help reduce the growth of breast cancer linked to obesity.
The research was presented at ENDO 2025, the Endocrine Society’s annual meeting in San Francisco. Tirzepatide is already approved under the brand names Mounjaro (for diabetes) and Zepbound (for obesity).
“Obesity is a major risk factor for breast cancer,” said Amanda Kucinskas, a Ph.D. candidate at the University of Michigan and lead author of the study. “While this is early data from a mouse study, our results show that these new anti-obesity drugs could potentially help reduce breast cancer risk or improve outcomes in people with obesity.”
Previous research has shown that breast cancer outcomes tend to be worse in people with obesity. Weight loss can improve those outcomes, but losing weight through diet and exercise alone is often difficult to maintain.
Tirzepatide belongs to a newer class of highly effective medications that target GLP-1 and GIP receptors, which help regulate blood sugar and appetite.
In this study, the researchers tested tirzepatide in 16 mice that were made obese by feeding them a high-fat diet. The mice were kept in a warm environment to simulate conditions that promote weight gain.
Starting at 32 weeks of age, half of the mice were given tirzepatide injections every other day for 16 weeks, while the other half received a placebo. Tumor growth was measured twice a week.
The results were promising. Mice that received tirzepatide lost about 20% of their body weight and fat, mainly through a reduction in fat tissue. This weight loss was similar to what has been observed in human clinical trials using the drug. More importantly, the drug also significantly reduced tumor size compared to the control group.
At the end of the study, researchers found that tumor size was strongly linked to overall body weight, total fat mass, and fat stored in the liver. These findings suggest that reducing body fat may help slow breast cancer growth in people with obesity.
“These are early findings, but they give us hope that tirzepatide might not just help with weight loss—it could also improve breast cancer outcomes,” Kucinskas said.
The team is continuing their research in partnership with Dr. Steve Hursting’s lab at the University of North Carolina at Chapel Hill. Their goal is to understand whether the drug’s effects on tumors are due only to weight loss or if tirzepatide has direct effects on cancer cells as well.
If you care about breast cancer, please read studies about how eating patterns help ward off breast cancer, and soy and plant compounds may prevent breast cancer recurrence.
For more health information, please see recent studies about how your grocery list can help guard against cancer, and a simple way to fight aging and cancer.
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