Anti-Obesity Drug Slows Breast Cancer Growth in Mice

Tirzepatide shows promise in reducing tumor size and fat mass

Early research suggests that tirzepatide, a medication already used for diabetes and obesity, may also help slow the growth of breast cancer linked to obesity. The study, conducted on mice, offers a potential new avenue for addressing obesity-related cancer risks.

Key Development

According to a study to be presented at ENDO 2025, the Endocrine Society’s annual meeting, the drug tirzepatide, known as Mounjaro for diabetes and Zepbound for obesity, significantly reduced the growth of breast cancer associated with obesity in a mouse model. Amanda Kucinskas, a Ph.D. candidate working in the labs of Drs. Erin Giles and Kanakadurga Singer at the University of Michigan, stated that their “studies in mice suggest that these new anti-obesity drugs may be a way to reduce obesity-associated breast cancer risk or improve outcomes.”

Study Details

The study involved feeding mice a high-fat diet to induce obesity, then treating them with either tirzepatide or a placebo. Researchers tracked tumor volumes and body composition over 16 weeks. The mice treated with the anti-obesity drug experienced a roughly 20% reduction in both body weight and body fat.

Furthermore, the research team observed that the anti-obesity drug led to reduced tumor volumes in comparison to the control group. At the conclusion of the study, a significant correlation was found between tumor volume and factors such as body weight, total adipose mass, and the quantity of fat stored in the liver.

Obesity and Breast Cancer

Obesity is a known risk factor for breast cancer, with existing data indicating that individuals with obesity often experience poorer outcomes. Weight loss has been shown to improve these outcomes, but traditional methods can be challenging. Statistics show that in the United States, about 42% of adults have obesity (CDC, 2024), highlighting the need for effective interventions.

Tirzepatide’s Mechanism

Tirzepatide targets GLP-1 (glucagon-like peptide 1) and GIP (glucose-dependent insulinotropic polypeptide) receptors. The researchers aimed to determine whether tirzepatide could specifically reduce breast cancer growth associated with obesity.

Future Research

Kucinskas noted, “While these are very preliminary results, they suggest that this new anti-obesity drug may also have a beneficial impact on breast cancer outcomes.” Further investigations are underway in collaboration with Dr. Steve Hursting’s lab at the University of North Carolina at Chapel Hill to distinguish the weight loss effects of tirzepatide from its potential tumor-specific impacts.