FDA approves Zytiga for late-stage prostate cancer

FDA has approved abiraterone acetate (Zytiga, Centocor Ortho Biotech), an oral, once-daily medication for use in combination with prednisone for the treatment of men with metastatic castration-resistant prostate cancer who have received prior chemotherapy containing docetaxel.

In prostate cancer, the male sex hormone testosterone stimulates prostate tumors to grow. Drugs or surgery are used to reduce testosterone production or to block the effects of testosterone. However, sometimes prostate cancer can continue to grow even when testosterone levels are low. Men with these cancers are said to have castration-resistant prostate cancer.

Zytiga targets cytochrome P450 17A1 (CYP17A1), which plays an important role in the production of testosterone. The drug works by decreasing the production of this hormone, which would stimulate cancer cells to continue growing.

The application was reviewed under FDA’s priority review program. Zytiga is being approved ahead of its June 20, 2011, regulatory goal date.

“[Zytiga] is in a new class of drugs that inhibits prostate cancer growth,” Mary B. Todd, DO, Zytiga global medical affairs leader, Janssen Global Services, LLC, told Formulary. “It is predominately going to be administered in the outpatient setting, which will eliminate administration costs associated with cabazitaxel injection.”

Zytiga’s safety and effectiveness were established in a phase 3, randomized, placebo-controlled, multicenter study of 1,195 patients with late-stage castration-resistant prostate cancer who had received prior treatment with docetaxel chemotherapy. Patients received either Zytiga once daily in combination with prednisone 2 times a day or a placebo twice daily in combination with prednisone.

Results of this study showed that at prespecified interim analysis, treatment with Zytiga in combination with prednisone resulted in a 35% reduction in the risk of death (14.8 months vs 10.9 months [HR= 0.646; 95% CI, 0.543, 0.768; P<.0001]) and a 3.9-month difference in median survival compared to placebo plus prednisone. In an updated analysis, results were consistent with those from the interim analysis, with a 4.6-month difference between the 2 arms in median survival (15.8 months vs 11.2 months [HR=0.74]).

At a predetermined number of events in the study, an interim analysis was conducted and it was determined that efficacy had been demonstrated. 

The most commonly reported side effects in patients receiving Zytiga included joint swelling or discomfort, low levels of potassium in the blood, fluid retention (usually of the legs and feet), muscle discomfort, hot flashes, diarrhea, urinary tract infection, cough, high blood pressure, heartbeat disorders, urinary frequency, increased nighttime urination, upset stomach or indigestion, and upper respiratory tract infection.