February 06, 2015
2 min read

Abiraterone acetate plus prednisone improved OS in certain patients with prostate cancer

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The addition of abiraterone acetate to prednisone significantly improved survival and delayed disease progression among men with metastatic castration-resistant prostate cancer who had not undergone chemotherapy, according to results of an international phase 3 study.

“These results also show the longest recorded median survival for a population of patients with castration-resistant prostate cancer at over 34 months, which is a reflection of not only the efficacy of abiraterone, but of the progress being made against this disease with the sequential use of new agents,” Charles J. Ryan, MD, associate professor of medicine and urology at Helen Diller Family Comprehensive Cancer Center at the University of California, San Francisco, told HemOnc Today.

Charles J. Ryan, MD

Charles J .Ryan

Abiraterone acetate is a less than fully active version of abiraterone (Zytiga, Janssen), an inhibitor of the cytochrome P450 c17 enzyme complex that helps produce androgen.

The COU-AA-302 trial included 1,088 asymptomatic or mildly symptomatic patients with chemotherapy-naive, metastatic castration-resistant prostate cancer.

Ryan and colleagues randomly assigned half of the patients to 1,000 mg abiraterone acetate daily plus 5 mg prednisone twice daily. The remaining patients received placebo plus prednisone.

An interim analysis of the COU-AA-302 trial showed abiraterone plus prednisone improved PFS in chemotherapy-naive patients with metastatic castration-resistant prostate cancer. In the final analysis, researchers assessed OS, time to opiate use and time to use of other subsequent therapies.

Median follow-up was 49.2 months (range, 47-51.8 months). At the time of final analysis, 8% of patients in the abiraterone acetate group were still receiving treatment, whereas no patients from the placebo group were still being treated. However, 238 patients (44%) in the placebo group had crossed over to abiraterone acetate treatment.

A lower percentage of patients in the abiraterone acetate group died during the study period (65% vs. 71%).

Median OS was 34.7 months (95% CI, 32.7-36.8) in the abiraterone acetate arm vs. 30.3 months (95% CI, 28.7-33.3) in the placebo arm (HR=0.81; 95% CI, 0.7-0.93).

After adjustments for the crossover effect, researchers observed an even greater reduction in risk for death among patients who received abiraterone acetate (HR=0.74; 95% CI, 0.6-0.88).

Median time to necessitation of opiate use for prostate cancer-related pain also was higher in the abiraterone acetate group (33.4 months vs. 23.4 months; HR=0.72; 95% CI, 0.61-0.85).

Patients in the abiraterone acetate group experienced higher rates of certain grade 3 or grade 4 adverse events, including cardiac disorders (8% vs. 4%), increased alanine aminotransferase (6% vs. <1%) and hypertension (5% vs. 3%).

 “These final results will put to rest any doubt that abiraterone benefits patients in this clinical state,” Ryan said. “[This] may increase the number of countries in which the therapy becomes available, and will thus allow this very effective therapy to reach more patients who need it.” – by Anthony SanFilippo 

Charles J. Ryan, MD, can be reached at Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, 1600 Divisadero St., MZ Bldg A, San Francisco, CA 94143; email: charles.ryan@ucsf.edu

Disclosure: The researchers report employment relationships with, research/grant funding from, consultant/advisory roles with, stock ownership in and honoraria from AbbVie, Algeta, Amgen, Aragon, Astellas, AstraZeneca, Bayer, BHR Pharma, BNIT Therapeutics, Bristol-Myers Squibb, Chiltern International, Dendreon, Exelixis, Ferring, Genentech, GlaxoSmithKline, GTX, ImClone, Janssen, Johnson & Johnson, Medivation, Merck, Millennium, Novartis, OncoGenex, Orion, Pfizer, Roche, Sanofi and Teva.