Antiandrogen therapy in metastatic male breast cancer: results from an updated analysis in an expanded case series

Male breast cancer is a rare disease treated as hormone receptor-positive female breast cancer. The characterization of breast cancer at the molecular level has lately revealed gender-related differences. As the androgen receptor is emerging as a potential oncogenic driver in male breast cancer, we analyzed efficacy data from metastatic patients treated with antiandrogens. We evaluated the activity of cyproterone acetate, either as a monotherapy or combined with a GnRH analog, in 36 metastatic male breast cancer patients. Fourteen patients were treated with cyproterone acetate as monotherapy and 22 patients with complete androgen blockade. We recorded 4 complete responses and 15 partial responses, for an overall response rate of 52.8 % (95 % CI, 36.5-69.4). Stable disease was reported in 11 patients. Median PFS was 8.9 months (95 % CI, 6.1-11.7), and median OS was 24.3 months (95 % CI, 22.5-26.1). Data on androgen receptor expression were available for 7 patients. All the 4 patients with androgen receptor-expressing tumors had a clinical benefit, including a patient with an estrogen receptor-negative disease. Conversely, none of the 3 patients with androgen receptor-negative tumors had a tumor response. Antiandrogen-based therapy showed efficacy in metastatic male breast cancer patients. Our results encourage considering antiandrogens in the therapeutic continuum, especially if supported by androgen receptor expression.