Role of androgen excess in the development of estrogen receptor-positive and estrogen receptor-negative breast cancer

The androgen-excess theory posits a central role of androgens in promoting breast cancer development. At first glance, this appears to contradict the currently accepted central role of estrogens in this process, but as we will show, the apparent contradiction is not a real one. In the present article, we review the mechanisms by which androgen excess may stimulate cancer growth in different subsets of estrogen receptor-positive and estrogen receptor-negative tumors. We also propose an endocrine classification of postmenopausal breast cancer based on the simultaneous evaluation of a patient's serum testosterone levels and the estrogen receptor status of the tumor. This classification identifies several different subsets of tumors and may have important clinical implications.