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Enzalutamide Outperforms Bicalutamide in 2 Trials of Prostate Cancer

September 2015, Vol 6, No 8

New Orleans, LA—Enzalutamide (Xtandi) outperformed bicalutamide (Casodex) in separate phase 2 clinical trials of men with prostate cancer, according to data presented at the 2015 American Urological Association annual meeting.

Enzalutamide was associated with long­er progression-free survival (PFS) and a greater benefit in health-related quality of life (QOL) compared with bicalutamide in men with metastatic castration-resistant prostate cancer (CRPC) in a trial known as TERRAIN, said Arnauld A. Villers, MD, PhD, Professor of Urology, University of Lille, France.

The patients had asymptomatic or mildly symptomatic metastatic CRPC that had progressed after treatment with a luteinizing hormone-releasing hormone analog or after surgical castration. The 375 patients were randomized to enzalutamide 160 mg daily or to bicalu­tamide 50 mg daily.

The median PFS was 15.7 months in the enzalutamide arm compared with 5.8 months in the bicalutamide arm. “The separation between the 2 curves was seen early, at 3 months,” said Dr Villers.

At week 13, 82% of patients in the enzalutamide arm versus 21% of patients in the bicalutamide arm had a prostate-specific antigen (PSA) decrease of ?50%; in addition, the percentage of patients with a PSA decrease of ?90% was 56% with enzalutamide versus 5% with bicalutamide. “Half of the patients in the enzalutamide arm reached a ?90% decrease in PSA by month 6,” Dr Villers said.

Enzalutamide was also significantly superior to bicalutamide in 5 of 7 QOL domains. QOL was maintained for a significantly longer time in the enzalutamide group, said Dr Villers.

Exposure to enzalutamide was double that seen with bicalutamide, a median of 11.7 months versus 5.8 months, respectively. The rates of serious adverse events were 31% in the enzalutamide arm and 23% in the bicalutamide arm. There were 3 seizures overall—2 in the enzalutamide arm and 1 in the bicalu­tamide arm.

In a second randomized phase 2 study known as STRIVE, enzalutamide was superior to bicalutamide as an add-on to androgen-deprivation therapy in men with nonmetastatic CRPC or meta­static CRPC, said Celestia S. Higano, MD, Professor of Medicine and Urology, University of Washington, Seattle.

In STRIVE, 396 patients were randomized to enzalutamide or bicaluta­mide at the same dosages that were used in TERRAIN.

The median PFS was 19.4 months in men randomized to enzalutamide versus 5.7 months in those randomized to bicalutamide, corresponding to a hazard ratio of 0.24 (P <.001). The time to PSA progression also favored enzalutamide, with the median time to PSA progression not reached in this arm at the time of data analysis compared with 8.3 months in the bicalutamide arm.

In the enzalutamide arm, 81% of patients had a ?50% decline in PSA level compared with only 31% in the bicalu­tamide arm, and 65% in the enzalutamide arm had a ?90% decrease in PSA compared with 9% in the bicalutamide arm.

“The enzalutamide arm is superior to the bicalutamide arm whether it’s an M0 [nonmetastatic CRPC] or M1 [metastatic CRPC] population on both the primary and key secondary end points,” said Dr Higano.

The median durations of treatment were 14.7 months in the enzalutamide arm versus 8.4 months in the bicalu­tamide arm.

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