Weight loss medication Mounjaro may potentially diminish breast cancer tumors, according to a recent study.
In a groundbreaking study presented at ENDO 2025, the Endocrine Society's annual meeting, researchers have discovered that a new GLP-1 drug, Tirzepatide, may hold the key to reducing the risk of obesity-associated breast cancer and improving outcomes for those already diagnosed.
Dr. David A. Taylor, the researcher behind the study at the University of Michigan, and his team focused on 16 young mice with breast cancer. Half of the mice were fattened up and given Tirzepatide, while the other half received a placebo, every other day for 16 weeks.
The results were striking. Mice that received Tirzepatide shed about 20% of their body weight and saw their breast cancer tumors decrease significantly. As the mice lost weight, the fat stored in their livers also decreased, leading to a corresponding shrinkage of their tumors.
Obesity is a significant risk factor for breast cancer, as excess abdominal fat can lead to higher estrogen levels. This hormonal imbalance promotes breast cancer development. Tirzepatide's potential benefits, according to study author Amanda Kucinskas, could be a game-changer in this regard.
Tirzepatide is already used for diabetes and obesity, known for being often better tolerated than other GLP-1 meds due to less nausea and vomiting and more weight loss. It mimics the GLP-1 hormone and also mimics the effects of GIP, a gut hormone that stimulates insulin release and influences fat storage and appetite.
However, it's important to note that the results are very preliminary, Kucinskas noted. Further research is needed to fully understand Tirzepatide's mechanisms and its potential impact on breast cancer.
Dr. Robert Decotiis, a clinical weight loss specialist, shared his observations. In his practice, he's seen all secondary benefits from GLP-1 drugs occur in patients who experienced significant reduction in fat. He urged, "Hold on to your hats and buckle up as this category of drug grows."
Breast cancer is the most commonly diagnosed cancer in women worldwide, besides skin cancer. With these promising findings, Tirzepatide could potentially revolutionise the treatment and prevention of this disease.
While GLP-1 meds have shown great promise, it's crucial to remember that side effects can include gastrointestinal distress, hair loss, skin pain, blindness, and behavioural changes (in rare cases). As with any medical treatment, it's essential to discuss the risks and benefits with a healthcare provider.
This research offers a glimmer of hope for those affected by breast cancer and obesity, and the field eagerly awaits further developments in this exciting area of medicine.
