* Approval comes three months early
* Improved median overall survival by 4.8 months in trial
* Label warns of seizure risk
* Wholesale price set at $7,450 per month
* Medivation shares rise 7.6 percent (Adds comments, details, updates share price)
By Deena Beasley
Aug 31 (Reuters) - A novel prostate cancer drug developed by Medivation Inc and Astellas Pharma Inc has been approved by the U.S. Food and Drug Administration for men whose cancer has spread despite treatment with hormone therapy and chemotherapy, the agency said on Friday.
Approval of the pill, to be sold under the brand name Xtandi, comes three months ahead of the agency's late-November decision deadline and sent shares of Medivation up 7.6 percent.
Wall Street analysts, on average, have forecast Medivation's sales of the drug at $1.2 billion by 2017, according to Thomson Pharma.
Xtandi, or enzalutamide, is one of a new class of drugs known as androgen inhibitors, designed to interfere with the ability of testosterone to bind to prostate cancer cells. Testosterone is the male hormone that fuels prostate cancer cell growth.
Medivation said it would begin selling the drug in the United States in mid-September at a wholesale price of $7,450 for a 30-day supply. Trial patients, on average, used the drug for eight months, the company said.
Medivation and Astellas, which have also filed for European approval, reported in November that a pivotal study of the drug had been stopped early after it became clear that it improved median overall survival by 4.8 months compared with a placebo.
The pill is also being tested in men with earlier stage prostate cancer, but Medivation has not said when those results are expected.
"The real opportunity for Xtandi is in pre-chemotherapy," Sanford Bernstein analyst Geoffrey Porges said in a research note.
He estimated that 18,000 to 20,000 U.S. prostate cancer patients receive chemotherapy every year and 4,000 to 5,000 eventually progress to other treatments.
"I am confident that this is only the beginning of success stories with this agent and that it will be used in earlier stages of prostate cancer in the near future," Dr. E. David Crawford, head of the urologic oncology department at the University of Colorado Health Sciences Center and chairman of the Prostate Conditions Education Council, said in a statement.
The FDA last year approved Johnson & Johnson's Zytiga, which is designed to work inside cancer cells to block testosterone production.
"The need for additional treatment options for advanced prostate cancer continues to be important for patients," Richard Pazdur, director of hematology and oncology products at the FDA's drug evaluation and research center, said in a statement. "Xtandi is the latest treatment for this disease to demonstrate its ability to extend a patient's life."
Xtandi "should have comparable or higher sales than Zytiga because it appears to have superior efficacy and had no serious adverse events in clinical trials," said ThinkEquity analyst Kimberly Lee.
Zytiga's worldwide sales rose about $32 million to $232 million in the second quarter from the first quarter.
Prostate cancer kills about 250,000 men a year globally and is the second most common cause of cancer death in men in the United States, after lung cancer.
The most common side effects seen with Xtandi were weakness, fatigue and back pain. The FDA said seizures occurred in about 1 percent of patients and they were taken off the therapy.
The FDA required that Medivation conduct a post-marketing study to further determine the seizure risk of Xtandi.
Medivation said the FDA approval and European regulatory filing trigger milestone payments from Astellas of $35 million, 10 percent of which it is obligated to pay to the University of California, Los Angeles under a licensing agreement.
Shares of Medivation gained $7.44, or 7.6 percent, to $104.86 on Nasdaq.
Shares of Japan-based Astellas closed down less than a percentage point at 3,820 yen in Tokyo, ahead of the announcement. (Additional reporting by Ransdell Pierson and Michele Gershberg; Editing by Leslie Gevirtz, Tim Dobbyn and Dan Grebler)