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Enzalutamide (Xtandi) More Effective Than Bicalutamide (Casodex) in Prostate Cancer Trial

Treatment improves survival in mid-stage study

Positive results have been reported from the phase II STRIVE trial comparing enzalutamide (Xtandi, Astellas Pharma/Medivation, Inc.) with bicalutamide (Casodex, AstraZeneca) in men with nonmetastatic or metastatic castration-resistant prostate cancer (CRPC).

The study achieved its primary endpoint by demonstrating a statistically significant increase in progression-free survival (PFS) for enzalutamide compared with bicalutamide (hazard ratio, 0.24; P < 0.0001). Median PFS was 19.4 months in the enzalutamide group compared with 5.7 months in the bicalutamide group.

The median time on treatment in the STRIVE trial was 14.7 months in the enzalutamide group compared with 8.4 months in the bicalutamide group. Serious adverse events (AEs) were reported in 29.4% of enzalutamide-treated patients and in 28.3% of bicalutamide-treated patients. Grade-3 or higher cardiac adverse events were reported in 5.1% of enzalutamide-treated patients compared with 4.0% of bicalutamide-treated patients. One seizure was reported in the enzalutamide-treated group and none in the bicalutamide-treated group. The most common AEs noted more frequently in enzalutamide-treated patients than in bicalutamide-treated patients included fatigue, back pain, hot flush, falls, hypertension, dizziness, and decreased appetite.

STRIVE was the second of two head-to-head studies comparing enzalutamide with bicalutamide, following the TERRAIN trial.

The STRIVE study enrolled 396 CRPC patients in the U.S. A total of 257 patients had metastatic prostate cancer, and 139 patients had nonmetastatic prostate cancer. In both groups of patients, their disease had progressed despite treatment with a luteinizing hormone-releasing hormone (LHRH) analogue or after surgical castration. The primary endpoint of PFS was defined as the time from randomization to radiographic (bone or soft-tissue) progression, PSA progression (defined by Prostate Cancer Working Group 2 criteria), or death due to any cause, whichever occurred first. The trial was designed to evaluate enzalutamide at a dose of 160 mg taken once daily compared with bicalutamide at a dose of 50 mg taken once daily, the approved dose in combination with an LHRH analogue.

The phase II TERRAIN trial enrolled 375 patients in North America and Europe. All of the patients had metastatic prostate cancer that had progressed despite treatment with an LHRH analogue or after surgical castration. PFS, the study’s primary endpoint, was defined as the time from randomization to centrally confirmed radiographic progression, skeletal-related events, the initiation of new antineoplastic therapy, or death, whichever occurred first. The study was designed to evaluate enzalutamide at a dose of 160 mg taken once daily compared with bicalutamide at a dose of 50 mg taken once daily, the approved dose in combination with an LHRH analogue.

Xtandi (enzalutamide) is approved by the FDA for the treatment of patients with metastatic CRPC. It is an androgen receptor inhibitor that acts on three different steps in the androgen receptor signaling pathway.

Source: Astellas Pharma; April 2, 2015.

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