Androgen receptor inhibitor shows significant PFS increase

April 6, 2015

Recent phase II results point to the efficacy of the prostate cancer agent enzalutamide (XTANDI) when compared with bicalutamide (Casodex).

The androgen receptor inhibitor enzalutamide (XTANDI) demonstrated a statistically significant increase in progression-free survival (PFS) in men with non-metastatic or metastatic castration-resistant prostate cancer compared with bicalutamide (Casodex), according to recent phase II trial results.

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The phase II STRIVE trial enrolled 396 castration-resistant prostate cancer patients in the U.S. The trial randomized 257 patients with metastatic prostate cancer and 139 patients with non-metastatic prostate cancer whose disease progressed despite treatment with a luteinizing hormone-releasing hormone (LHRH) analogue therapy or following surgical castration. The primary endpoint of the trial was PFS, defined as 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 occurs first.

The trial was designed to evaluate enzalutamide, 160 mg once daily, versus bicalutamide, 50 mg once daily, the approved dose in combination with a LHRH analogue.

Median PFS was 19.4 months in the enzalutamide group compared with 5.7 months in the bicalutamide group (Hazard Ratio=0.24; 95% Confidence Interval, 0.18-0.32; p<.0001), according to a news release from Medivation, Inc. and Astellas Pharma Inc.

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Among the other findings reported:

  • The median time on treatment in the STRIVE trial was 14.7 months in the enzalutamide group versus 8.4 months in the bicalutamide group.

  • Serious adverse events were reported in 29.4% of enzalutamide-treated patients and 28.3% of bicalutamide-treated patients.

  • Grade 3 or higher cardiac adverse events were reported in 5.1% of enzalutamide-treated patients versus 4.0% of bicalutamide-treated patients.

  • One seizure was reported in the trial in the enzalutamide-treated group and none in the bicalutamide-treated group.

The most common side effects noted more frequently in the enzalutamide-treated versus bicalutamide-treated patients included fatigue, back pain, hot flush, fall, hypertension, dizziness, and decreased appetite, consistent with the known safety profile of enzalutamide.

"These results demonstrate the potential for enzalutamide to provide a longer duration of disease control compared with bicalutamide in the studied patient population," said STRIVE co-principal investigator David F. Penson, MD, MPH, of Vanderbilt University Medical Center, Nashville, TN. 

Enzalutamide is currently approved by the FDA for the treatment of patients with metastatic castration-resistant prostate cancer.

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