SAN FRANCISCO—The androgen-receptor blocker enzalutamide is associated with delayed tumor progression and improved survival among men with metastatic castration-resistant prostate cancer (mCRPC), according to an analysis of data from the double-blind, placebo-controlled phase 3 PREVAIL study. The analysis was presented during the 2014 Genitourinary Cancers Symposium.
Enzalutamide plus androgen-deprivation therapy was well tolerated and offered “meaningful clinical benefit” to men with previously untreated mCRPC, said lead study author Tomasz Beer, MD, FACP, of the Oregon Health & Science University’s Knight Cancer Institute in Portland, OR.
The trial was halted prematurely following an interim analysis that demonstrated enzalutamide efficacy, Dr. Beer noted.
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“Enzalutamide is likely to become an important new treatment option that has a significant impact on progression of prostate cancer,” Dr. Beer said. “If approved for this indication, it will become an important standard option for use before chemotherapy in patients with asymptomatic or minimally symptomatic advanced prostate cancer.”
A total of 1,717 men with previously untreated mCRPC were randomly assigned to receive enzalutamide (160 mg/day; n = 872) or placebo (n = 845), plus standard hormone therapy, he said.
Enzalutamide was associated with a significant 29% reduction in mortality (hazard ratio [HR], 0.706; P < 0.0001) and delayed median time to chemotherapy by 17 months (28.0 vs. 10.8 months; HR, 0.35; P < 0.0001), Dr. Beer reported.
“Enzalutamide reduced the risk of radiographic progression by 81%” (HR, 0.186; P < 0.0001), Dr. Beer reported. Radiographic progression was defined as new lesions on bone scans or growth of existing metastatic tumors.
Enzalutamide was well tolerated, Dr. Beer noted. Discontinuations due to adverse events were 6% in both the treatment and the placebo study arms. Time to first grade 3 or higher adverse events was 22.3 months for patients taking enzalutamide compared with 13.3 months in the placebo group. The most common adverse events—affecting 20% or more of patients receiving enzalutamide and 2% or more of patients receiving placebo—included fatigue (36% vs. 26% in the placebo group); back pain (27% vs. 22%); constipation (22% vs. 17%); and arthralgia (20% vs. 16%).
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“Most of these were grade 1 or 2,” Dr. Beer said, noting that the observation period for the enzalutamide arm was “three times longer” than the placebo arm (median, 17.1 vs. 5.4 months).
“Enzalutamide significantly reduced the risk of death … and delayed the progression of metastatic disease,” he concluded. “Enzalutamide, an oral once-daily medication, was well-tolerated over a prolonged treatment period.”
The findings are “an important study for our field, to be sure,” commented panel moderator Charles J. Ryan, MD, of the Helen Diller Family Comprehensive Cancer Center at UC San Francisco.
The 2014 Genitourinary Cancers Symposium is sponsored by the the American Society of Clinical Oncology (ASCO), the American Society for Radiation Oncology (ASTRO), and the Society of Urologic Oncology (SUO).