Aromatase inhibitors with or without luteinizing hormone–releasing hormone agonist for metastatic male breast cancer: report of four cases and review of the literature

The roles of aromatase inhibitors (AIs) and luteinizing hormone–releasing hormone (LH–RH) agonists in the management of male breast cancer remain uncertain, with no reports in Japanese men. We report four Japanese male patients with metastatic breast cancer treated with AIs with or without an LH–RH agonist, and consider the relationship between treatment effect and estradiol (E2) concentration. Three patients were initially treated with AI alone after selective estrogen receptor modulators (SERMs), and one received AIs plus an LH–RH agonist after a SERM. Two patients treated with an AI alone responded, one patient with E2 levels below the lower assay limit and the other with levels above the limit. The other treated with an AI alone experienced progression regardless of the E2 levels below the lower assay limit, however, responded after the addition of an LH–RH agonist. E2 concentrations were related to the efficacy of treatment in one patient. The patient initially treated with an AI plus an LH–RH agonist also responded. No grade 3 or 4 adverse events were observed in any of the patients treated with AIs with or without an LH–RH agonist. AIs with or without an LH–RH agonist offer an effective treatment option for hormone receptor-positive metastatic male breast cancer.