Medivation, Inc., a biopharmaceutical company, and Astellas Pharma Inc., a comopany dedicated to improving the health of people around the world, have enrolled the first patient in a global phase II clinical trial evaluating enzalutamide as a single agent for the treatment of advanced, androgen receptor (AR)-positive, triple-negative breast cancer (TNBC). Medivation is conducting this study under its agreement with Astellas.

"The initiation of this phase II study marks an important milestone as we expand our enzalutamide development program beyond prostate cancer to explore the clinical efficacy of enzalutamide in triple-negative breast cancer, where there is a significant unmet medical need," said David Hung, MD, president and chief executive officer of Medivation, Inc. "We plan to present the results from the Phase 1 study in breast cancer at an upcoming scientific conference."

The phase II open label, single-arm, multi-centre trial plans to enrol approximately 80 patients with AR-positive, TNBC at sites in the United States, Canada and Europe. The primary endpoint of the trial is clinical benefit rate, defined as the proportion of patients with a best response of complete response, partial response or stable disease at = 16 weeks. All patients will receive enzalutamide at a dose of 160 mg to be taken orally once daily.

TNBC is a type of cancer which does not express any of the three most commonly targeted receptors in breast cancer: estrogen, progesterone and HER2. TNBC remains an area of significant unmet medical need. Currently, there are no approved targeted therapies for these patients, who are typically treated with multiple regimens of chemotherapy. AR-positive breast cancer is a recently-identified subtype of TNBC that can express high levels of the androgen receptor.

Enzalutamide is an androgen receptor inhibitor that acts on different steps in the androgen receptor signalling pathway. Enzalutamide has been shown to competitively inhibit androgen binding to androgen receptors, and inhibit androgen receptor nuclear translocation and interaction with DNA.

XTANDI is indicated for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) who have previously received docetaxel.