The FDA has expanded the indication for abiraterone acetate (Zytiga tablets) in combination with prednisone for the treatment of men with metastatic castration-resistant prostate cancer (mCRPC). The drug, which reduces the production of testosterone, was originally approved in April 2011, for use in men whose prostate cancer progressed after treatment with the chemotherapy agent docetaxel.
Approval for the new indication was granted under the FDA’s priority-review program, which provides for an expedited 6-month review for drugs that may offer major advances in treatment or provide a treatment where no adequate therapy exists. The trial upon which the expanded Zytiga approval was based centered on men with CRPC that had metastasized to the bone, soft tissue, or lymph nodes.
None of the men in the study had received cytotoxic chemotherapy, none had moderate or severe cancer pain, and none were using opiates for cancer pain. All participants had had a prior orchiectomy or continued to receive a gonadotropin-releasing hormone analog. Patients were randomized to receive abiraterone acetate plus prednisone (N=546) or placebo plus prednisone (N=542).
Abiraterone acetate treatment improved radiographic progression-free survival (rPFS): The median rPFS, which was 8.3 months in the placebo arm, had not yet been reached for those receiving the study drug at the time of reporting. At the prespecified third interim analysis, median overall survival was 35.3 months for the abiraterone acetate group, compared with 30.1 months in the placebo arm.
An evaluation of 1,333 men with mCRPC who received abiraterone acetate plus prednisone and 934 men who received placebo plus prednisone in this and another pivotal trial revealed that the most common adverse reactions (occurring in at least 10% of patients) were fatigue, joint swelling or discomfort, edema, hot flush, diarrhea, vomiting, cough, hypertension, dyspnea, urinary tract infection, and contusion. Grade 3 or grade 4 adverse reactions occurred in 55% of patients receiving abiraterone acetate and in 50% of those receiving placebo.
The most common laboratory abnormalities, seen in more than 20% of patients, were anemia, elevated alkaline phosphatase, hypertriglyceridemia, lymphopenia, hypercholesterolemia, hyperglycemia, elevated AST, hypophosphatemia, elevated ALT, and hypokalemia.