Some patients with estrogen receptor–positive breast cancer experience treatment failure when using estrogen-blocking drugs. According to a study presented at the joint meeting of the International Society of Endocrinology and the Endocrine Society, estrogen receptors may depend on the androgen receptor in order to function. Even though the androgen receptor is expressed in the majority of prostate cancers, it is expressed in a majority of breast cancers as well, and Jennifer Richer, PhD, said that patients with breast cancer do not usually receive androgen receptor testing. Richer and her colleagues found that patients were 4.4 times more likely to have a relapse during treatment with tamoxifen, an estrogen-blocking drug, when the patient’s main tumor had a high ratio of androgen receptor–positive cells to estrogen receptor–positive cells. Since the receptor moves itself, as well as the hormone-bound to it inside of a cell’s nucleus (where the receptor carries out important tasks), the researchers hypothesized that the androgen receptor’s nuclear localization determines the estrogen receptor’s maximal activity. In response to this finding, Richer and colleagues tested enzalutamide, an anti-androgen drug used in prostate cancer therapy that prevents androgen receptors from entering the nucleus. It was found that enzalutamide inhibited tumor growth for both androgen- and estrogen-positive breast cancer.
Researchers believe they have discovered one reason why some women with estrogen receptor-positive breast cancer may respond poorly or only temporarily to estrogen-blocking drugs such as tamoxifen. Results of a new study, which was presented Saturday at the joint meeting of the International Society of Endocrinology and the Endocrine Society: ICE/ENDO 2014 in Chicago, point to a previously unrecognized role of the androgen receptor.