Newly approved as a treatment for prostate cancer, enzalutamide may be useful in combating breast cancer that evades other therapies, report researchers from the University of Colorado Cancer Center (CU Cancer Center) in Aurora, Colorado.

The FDA approved enzalutamide (Xtandi) in August 2012 for the treatment of men with metastatic castration-resistant prostate cancer who had previously received docetaxel. When enzalutamide was still in its experimental stages, this androgen receptor inhibitor was known as MDV-3100. Ten years ago, at the CU Cancer Center, Anthony Elias, MD, and Jennifer Richer, PhD, began using MDV-3100 in cell culture and animal models to test whether the androgen receptor was the pathway driving estrogen-positive breast cancer that responded poorly or only very temporarily to estrogen-blocking treatments.

According to a statement from the CU Cancer Center describing the work of Elias and Richer, 75% of all breast cancers and approximately 20% of triple-negative cases (estrogen receptor [ER]–negative, progesterone receptor [PR]–negative, and human epidermal growth factor receptor 2 [HER2]–negative) are, in fact, positive for the androgen receptor.

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Elias and Richer, whose work was presented at the CTRC-AACR San Antonio Breast Cancer Symposium in San Antonio, Texas, held December 4-8, 2012, have been conducting a phase I clinical trial to prove drug safety. They expect the study to soon convert to phase II, which will focus on demonstrating results regarding the effectiveness of enzalutamide in breast cancers that seem susceptible to anti-androgen therapy.