Mouse Study Shows Tirzepatide Slows Growth of Obesity-Related Breast Cancer

A recent study presented at ENDO 2025, the annual meeting of the Endocrine Society in San Francisco, has revealed promising findings on the effects of tirzepatide, an anti-obesity medication, on breast cancer in a mouse model. Known commercially as Mounjaro for diabetes and Zepbound for obesity, tirzepatide was found to significantly reduce breast tumor growth in mice that were made obese through a high-fat diet.

In this study, 16 nine-week-old C57BL/6 mice were fed a diet consisting of 40% fat to induce obesity. At 32 weeks, the obese mice received injections of tirzepatide or a placebo every other day for a period of 16 weeks, with tumor sizes measured twice weekly. The mice treated with tirzepatide experienced a weight and fat reduction of approximately 20%, mainly due to loss of adipose tissue, with a significant decrease in fat depot weights compared to untreated controls.

The key finding was that tumor volume was markedly smaller in the mice receiving tirzepatide. At the study’s conclusion, tumor size was closely linked to body weight, total adipose tissue, and liver fat content. These results suggest that tirzepatide, beyond its role in weight management, might have a beneficial impact on breast cancer outcomes, especially in cases linked to obesity.

"While these findings are preliminary, they indicate that anti-obesity drugs like tirzepatide may help reduce breast cancer risk or improve treatment results," explained study author Amanda Kucinskas, a Ph.D. candidate at the University of Michigan. The ongoing research aims to distinguish the effects of weight loss itself from those directly related to the tumor, collaborating with experts at the University of North Carolina.

Obesity is a known risk factor for poorer breast cancer prognosis, with weight loss often leading to better outcomes. However, traditional weight management methods face many challenges. The study highlights tirzepatide’s dual potential for weight reduction and cancer treatment, opening new avenues for research in obesity-related cancer therapies.