Days after regulators in Europe approved Astellas and Medivation's prostate cancer drug Xtandi, the companies have begun a mid-stage trial of the therapy in breast cancer.

The partners have announced enrollment of the first patient in a Phase II clinical trial evaluating Xtandi (enzalutamide) as a single agent for advanced, androgen receptor (AR)-positive, triple-negative breast cancer. Medivation, which is conducting the study, plans to enrol 80 patients with AR-positive, TNBC at sites in the USA, Canada and Europe, all of whom will receive enzalutamide, an androgen receptor inhibitor, at a dose of 160mg to be taken orally once-daily.

TNBC does not express any of the three most commonly targeted receptors in breast cancer - oestrogen, progesterone and HER2 - so remains an area of significant unmet medical need, Astellas and Medivation noted. Currently, there are no approved targeted therapies for these patients, who are typically treated with multiple regimens of chemotherapy.

David Hung, Medivation chief executive, said that starting the study "marks an important milestone as we expand our enzalutamide development program beyond prostate cancer". He added that the firm will present the results from the Phase I study in breast cancer at an upcoming scientific conference.