Since women with breast cancer treated with AIs represent a population at higher risk of metabolic disturbances, aim of the present study was to evaluate in a cohort of postmenopausal, nondiabetic, AI-treated women with breast cancer the effect of a single 60 mg dose of denosumab on parameters of glucose metabolism, including circulating levels of hepatic-released FGF21, a metabolic regulator with multiple effects on lipid and glucose metabolism. This evidence concerns the gene FGF21 and breast cancer.