Obesity has long been recognised as a significant risk factor for various cancers, including breast cancer, and the challenges associated with conventional weight loss methods are well-documented. However, recent groundbreaking research presented at ENDO 2025, the Endocrine Society’s annual meeting in San Francisco, California, highlights a promising new development in this area.
A study conducted in mouse models suggests that tirzepatide, a dual GLP-1 (glucagon-like peptide 1) and GIP (glucose-dependent insulinotropic polypeptide) receptor agonist, not only aids in substantial weight reduction but also significantly diminishes the growth of obesity-associated breast tumours. This dual-action approach could mark a pivotal shift in how obesity-related cancers are addressed, offering unexpected benefits beyond metabolic health.
Amanda Kucinskas, B.S., a Ph.D. candidate from the University of Michigan in Ann Arbor, Michigan, who is a lead author of the study, emphasised the preliminary yet compelling nature of these findings. She noted that while the data is still very early, their research in mice indicates that these novel anti-obesity medications may offer a strategy to lessen the risk of obesity-associated breast cancer or enhance outcomes for those affected. This aligns with existing evidence demonstrating that obesity can lead to poorer cancer prognoses compared to individuals of a healthy weight, and that weight loss generally improves these outcomes.
However, the difficulties in achieving and maintaining weight loss through traditional dieting methods often fall short, underscoring the potential importance of new pharmacological interventions.
Tirzepatide, marketed as Mounjaro for diabetes and Zepbound for obesity, operates by mimicking the effects of natural hormones that regulate appetite and blood sugar, thereby helping to reduce hunger and improve weight management. The UK’s National Health Service (NHS) has recently announced that Mounjaro (tirzepatide) will be made available as a new weight-loss injection to support individuals living with obesity, with prescriptions becoming available from late June 2025 as part of a phased rollout.
While the initial focus is on those with a high Body Mass Index (BMI) and specific co-morbidities, the broader implications of its use are gaining attention. People seeking more detailed information on how Mounjaro may impact breast cancer growth, especially in early studies, further insights are often available through resources that explore how weight loss drugs such as Mounjaro could potentially slow breast cancer progression in mice.
The mouse study, a pivotal component of this research, involved 16 C57BL/6 mice. These 9-week-old mice were fed a 40% high-fat diet and kept in a warm environment to induce obesity. At 32 weeks of age, the obese mice were then randomly divided into two groups: one received injections of tirzepatide every other day for 16 weeks, while the other received a placebo. Throughout this period, tumour volumes were meticulously measured twice weekly to track changes.
The results were notably encouraging. The anti-obesity drug led to an approximate 20% reduction in body weight and body fat in the treated mice, a figure comparable to the amount of weight loss observed in women using tirzepatide. This reduction was primarily attributed to a significant loss of adipose (fat) mass, with a notable decrease in adipose depot weights when compared to the control group. More critically, the anti-obesity drug also resulted in a significant reduction in tumour volume compared to the controls.
At the conclusion of the study, researchers established a strong correlation between tumour volume and body weight, total adipose mass, and the amount of fat stored in the liver, reinforcing the link between fat reduction and cancer outcome.
Kucinskas reiterated that these results, while preliminary, strongly suggest that tirzepatide could have a beneficial impact on breast cancer outcomes. To delve deeper into the mechanisms at play, ongoing studies are being conducted in collaboration with Dr. Steve Hursting’s laboratory at the University of North Carolina at Chapel Hill. These follow-up investigations aim to precisely differentiate between the effects of weight loss itself and any direct tumour-specific impacts of tirzepatide, which will be crucial for understanding the full therapeutic potential of this drug.
In the UK, the discussion around tirzepatide and its potential broader applications is gathering pace. NICE, the National Institute for Health and Care Excellence, has outlined how tirzepatide will be rolled out, noting that clinical trials have shown it to be more effective than diet and exercise alone, and even more so than semaglutide, another popular weight-loss medication. Patients in the SURMOUNT-4 trial, for instance, experienced an average body weight loss of 21% over 36 weeks . This further solidifies the drug’s efficacy in weight management, which now appears to have encouraging implications for cancer prevention and treatment, particularly in obesity-associated cases.
In conclusion, the findings from the ENDO 2025 study offer a compelling glimpse into a future where anti-obesity medications like tirzepatide could serve a dual purpose: tackling obesity and mitigating the risks and progression of associated cancers. While the research is still in its early stages and primarily conducted in mouse models, the consistent observation of reduced body fat and shrunken breast tumours provides a strong foundation for further investigation.
This exciting development highlights the evolving understanding of the complex interplay between metabolic health and cancer, potentially paving the way for innovative and integrated therapeutic strategies for obesity-related cancers. The continued research and clinical trials will be vital in translating these promising preclinical results into tangible benefits for human patients, potentially reshaping the landscape of cancer care in the context of obesity.