Clinical Implications of Mounjaro (Tirzepatide) for Breast Cancer Detection and Management: A Narrative Review.

Tirzepatide, marketed as Mounjaro, is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist that is widely used to treat type 2 diabetes and obesity. As more women presenting to screening and symptomatic breast clinics receive tirzepatide, questions have emerged regarding how rapid pharmacologic weight loss may influence breast lump detection, mammographic density, and breast cancer risk. This narrative review summarises tirzepatide pharmacology, its effects on adiposity, expected changes in breast composition with weight loss, oncologic data on breast cancer risk and outcomes, and radiological implications for mammography, ultrasound, and MRI. Randomised-trial data and meta-analyses currently show no clear evidence of increased breast cancer incidence with tirzepatide or GLP-1 receptor agonists. Preclinical studies in obesity-associated breast cancer models have demonstrated reduced mammary tumour progression following tirzepatide-induced weight loss and metabolic improvement; however, the clinical relevance of these findings remains uncertain. In the clinic, GLP-1 receptor agonist use in women with breast cancer has been associated with clinically meaningful weight loss without short-term safety signals. Weight loss decreases breast volume and subcutaneous fat, often making pre-existing benign lesions more palpable and altering mammographic density and parenchymal patterns, but available data do not indicate reduced imaging accuracy. Clinicians should maintain standard triple assessment, recognise that new palpable nodularity may reflect unmasked benign tissue, and reassure patients that current clinical evidence has not demonstrated an increased breast cancer risk associated with tirzepatide use. High-quality prospective imaging and oncology studies are needed to define long-term effects.