The Therapeutic Effect of Cyclin-Dependent Kinase 4/6 Inhibitor on Relapsed Ectopic Male Breast Cancer

Ectopic male breast cancer is very rare. Consequently, there is a lack of prospective clinical trials, and most recommendations for treatment are based on the experiences of clinicians and data from female breast cancer patients. The United States Food and Drug Administration has recently approved palbociclib combined with endocrine therapy for advanced male breast cancer because of the positive results of its use in metastatic female breast cancer. Therefore, it is worth considering cyclin-dependent kinase 4/6 inhibitors as alternatives to conventional chemotherapies for advanced male breast cancer patients with hormone receptor-positive and human epidermal growth factor receptor 2-negative cancers. The present case report introduces the use of palbociclib plus letrozole as first-line therapy for an elderly male patient with relapsed ectopic breast cancer, notwithstanding the limitations of the current national health insurance policy.