Medivation and partner Astellas Pharma are celebrating after the getting the green light for their eagerly-anticipated late-stage prostate cancer drug Xtandi.

The US Food and Drug Administration has completed a priority review and gave the thumbs-up to Xtandi (enzalutamide) some three months ahead of the product’s prescription drug user fee goal date of November 22. The approval is for the treatment of metastatic castration-resistant prostate cancer that has spread or recurred, even with medical or surgical therapy to minimise testosterone.

The approval is based on a study of 1,199 patients with mCRPC who had received prior treatment with docetaxel. The median overall survival for patients receiving Xtandi was 18.4 months, compared with 13.6 months for those on placebo.

Richard Pazdur, FDA director of the Office of Hematology and Oncology Products, said that "the need for additional treatment options for advanced prostate cancer continues to be important". He added that “Xtandi is the latest treatment for this disease to demonstrate its ability to extend a patient’s life".

As a post-marketing requirement, Medivation and Astellas will conduct an open-label safety study of Xtandi in patients who are at high risk for seizure, the data for which will be ready by 2019. The drug has also been filed with the European Medicines Agency.

Medivation chief executive David Hung said the approval "marks a significant accomplishment" and may analysts agree, as do investors. The biotech's shares reached their highest level, over $104, since they started trading in 1996.

Xtandi, an oral, once-daily androgen receptor inhibitor, will go up against Johnson & Johnson’s Zytiga (abiraterone) and Dendreon Corp’s infusion Provenge (sipuleucel-T). It will cost $7,450 a month and is widely expected to be a major blockbuster.