Triple-negative breast cancer: role of the androgen receptor.

The androgen receptor (AR), a member of the steroid hormone receptor family, is expressed in more than 70% of breast cancers and has been implicated in breast cancer pathogenesis. The role of the AR is of particular interest in patients with estrogen- and progesterone receptor negative and HER2-negative cancers, which represent approximately 25% of all breast cancers. The "triple-negative" subset of tumors generally has a more aggressive clinical course and does not benefit from conventional endocrine targeted therapies. However, emerging evidence suggests that the AR may serve as a therapeutic target for a subset of triple-negative breast cancers. Herein, we review the role of the AR in breast cancer tumorigenesis and current progress and future directions in the development of AR-targeted therapies.