By Elie Dolgin of Nature Medicine magazine
Men with advanced prostate cancer now have another treatment option, thanks to the approval August 31 by the U.S. Food and Drug Administration (FDA) of a pill that blocks androgen-receptor signaling and prolongs patient survival.
“To see activity in a post-hormone treated, post-chemotherapy treated prostate cancer population with a drug that doesn’t have myelosuppression [a decrease in blood cell production] and does has a very favorable safety profile is extremely exciting,” says Howard Scher, a prostate cancer specialist at the Memorial Sloan-Kettering Cancer Center in New York. “My patient who got the drug in July 2007 is still on it. I have chills actually. It’s pretty amazing.”
The newly approved agent—Xtandi (enzalutamide), developed by San Francisco’s Medivation and Japan’s Astellas Pharma—works by plugging up the receptors that bind androgens, including testosterone, to prevent those male hormones from fueling the growth of prostate cancer cells. In a phase 3 clinical trial involving around 1,200 men with prostate cancer that had spread despite prior chemo- and hormone-therapy, an international team led by Scher found that participants taking Xtandi lived a median of 18.4 months, compared to 13.6 months for those who received a placebo. The drug also significantly lowered levels of prostate-specific antigen and boosted the time of progression-free survival, with only minimal side effects of fatigue, diarrhea and rare seizures. The results were reported earlier this month in the New England Journal of Medicine.
“This is a very active drug,” says Andrew Armstrong, an oncologist at the Duke Cancer Institute in Durham, North Carolina, who was involved with the trial. “It’s active in the most refractory of patients, and it’s likely even more active in the earlier setting when patients aren’t as far along in their disease process.” Studies evaluating the drug in men with metastatic prostate cancer who have not yet received chemotherapy are ongoing.
According to Decision Resources, the prostate cancer drug market in the US is forecast to more than double over the next decade, increasing from $3.6 billion in 2010 to around $9 billion in 2020. Medivation’s drug is expected to compete most fiercely with Johnson & Johnson’s Zytiga (abiraterone), a pill that inhibits testosterone synthesis. Zytiga won US and European approval in 2011, and earned around $430 million in global sales in the first half of this year, half of which came from the US market.
Like Xtandi, Zytiga is only approved for men who have failed chemotherapy treatment. But this week J&J announced that it had won priority review status from the FDA for the company’s application to get Zytiga approved additionally for prostate cancer patients who have not yet undergone chemo. A decision is expected before the end of the year.