2. Role of the androgen receptor in triple-negative breast cancer

Triple-negative breast cancer (TNBC) accounts for 15% to 25% of breast-cancer diagnoses. TNBC expresses neither estrogen nor progesterone receptors, nor does it overexpress human epidermal growth factor type-2 receptor. It is an aggressive form of cancer and has not been a specific target of therapies for breast cancer. While it is initially sensitive to chemotherapy, TNBC has a high rate of relapse and poor prognosis after such chemotherapy. More effective therapeutic options for this subset of breast cancer are needed. Androgen receptor (AR) is expressed in one-third of TNBCs, and recent studies have clarified its action in breast cancer. AR-targeted therapy is one of the envisioned new therapies for TNBC; the therapeutic approach can involve the inhibition of androgen synthesis, use of non-androgenic AR-binding hormones, inhibition of co-regulators, activation of membrane AR, and reassessment of medroxyprogesterone acetate. These approaches are being evaluated in studies at the preclinical and phase II levels. Targeted therapies that improve outcome in patients with TNBC are expected to be developed in the near future. Correspondence/Reprint request: Dr. Yoshinari Ogawa, Department of Breast-Surgical Oncology, Osaka City General Hospital, 2-13-22, Miyakojima-hondori, Miyakojima-ku, Osaka, 534-0021, Japan E-mail: [email protected] Yoshinari Ogawa & Katsumi Ikeda 28