Pharm'Up 
A study unveiled at ENDO 2025, the Endocrine Society’s annual gathering in San Francisco, Calif., reveals that tirzepatide, marketed as Mounjaro for diabetes and Zepbound for obesity, inhibited obesity-related breast cancer progression in mice. The early findings were presented by Amanda Kucinskas, B.S., a Ph.D. candidate collaborating with Drs. Erin Giles and Kanakadurga Singer at the University of Michigan, Ann Arbor.
Kucinskas commented, “Obesity heightens breast cancer risk, and while our initial mouse data is promising, it indicates that these advanced anti-obesity medications might help reduce related cancer risks or improve prognosis.”
Studies have established that obesity correlates with poorer breast cancer outcomes compared to non-obese cases, with weight loss offering potential benefits. Yet, conventional weight loss strategies often encounter significant challenges. The research employed tirzepatide, a novel anti-obesity agent targeting GLP-1 and GIP receptors, to assess its effect on obesity-driven breast cancer.
The trial included 16 C57BL/6 mice, starting at 9 weeks old, fed a 40% high-fat diet in a warm setting to induce obesity. At 32 weeks, the obese mice were split into groups receiving either tirzepatide or a placebo every other day for 16 weeks, with tumor sizes tracked biweekly.
Findings indicated that tirzepatide lowered body weight and fat by approximately 20%, mirroring human weight loss trends, mainly through reduced adipose tissue. It also significantly decreased tumor volume compared to controls. By the study’s conclusion, tumor size was strongly associated with body weight, total fat mass, and liver fat content.
Kucinskas added, “Though preliminary, these results suggest tirzepatide could positively influence breast cancer outcomes in addition to aiding weight loss.”
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