Xtandi approved as first line prostate cancer treatment

Prostate cancer drug Xtandi has been given FDA approval for use as a first line treatment for metastatic castration-resistant prostate cancer (CRPC).

The new approval allows Astellas and Medivation's Xtandi to compete more directly with the other novel oral treatment for prostate cancer, Janssen's Zytiga (abiraterone), and will help cement its blockbuster prospects.

Xtandi (enzalutamide) was first approved in August 2012 for use in CRPC for patients who have already received docetaxel chemotherapy. Janssen's drug gained US approval for first line use in December 2012, and has since established itself as a market leader among new agents for the cancer.

However some analysts are predicting Xtandi could overtake its rival, reaching peak sales of up to $4 billion.

Metastatic CRPC is defined as a cancer that has spread beyond the prostate gland and has progressed despite treatment to lower testosterone (i.e., with a gonadotropin-releasing hormone (GnRH) therapy or with removal of the testes).

Xtandi has shown results in its phase 3 PREVAIL trial on a par with Zytiga. Men receiving Xtandi and GnRH therapy exhibited a statistically significant improvement in both overall survival and delayed time to radiographic progression or death as compared to those on placebo and GnRH therapy.

The Astellas and Medivation drug significantly reduced the risk of radiographic progression or death by 83% compared with placebo.

Xtandi reduced the risk of death by 29% compared with placebo, and also delayed time to initiation of chemotherapy and time to a skeletal related event.

Tomasz M. Beer, M.D., co-principal investigator of the PREVAIL study, deputy director of the Knight Cancer Institute and professor of medicine at Oregon Health & Science University hailed the drug's impressive data, including improved overall survival and significant delay to progression.

"In the PREVAIL trial, the median time to initiating chemotherapy was delayed by 17 months with enzalutamide treatment as compared to placebo, so the result is a meaningful period of time during which men have their disease controlled without the need for chemotherapy."

One slight cause for concern in regards to its safety profile emerged in the trials, with a small but significant number of seizures in patients receiving the drug. Seizure occurred in 0.9% of patients receiving Xtandi who previously received docetaxel and 0.1% of patients who were chemotherapy-naive.

Patients experiencing a seizure were permanently discontinued from therapy and all seizure events resolved, and has advised the same course of action for patients outside of trials. The company now says patients should be advised of the risk of engaging in any activity during which sudden loss of consciousness could cause serious harm to themselves or others.

Nevertheless, analysts say that Xtandi has advantages over Zytiga in its side-effect profile, and that patients are not required to also take prednisone, as they do with Zytiga.

The drug is also currently under review by Europe's medicines regulator the EMA.