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Chicago, IL—Patients with asymptomatic and mildly symptomatic chemotherapy-naïve metastatic castration-resistant prostate cancer had significantly improved radiographic progression-free survival (rPFS) and showed a strong trend for increased overall survival (OS) following treatment with abiraterone acetate plus prednisone compared with prednisone alone, according to second interim analysis results of a study1 presented here at the 2012 Annual Meeting of American Society of Clinical Oncology.
Abiraterone acetate also extended time patients had minimal or no symptoms and was safe, noted Charles J. Ryan, MD, UCSF Helen Diller Family Comprehensive Cancer Center, San Francisco, CA, on behalf of the COU-AA-302 study investigators. He pointed out there is a persistent unmet need in metastatic castration-resistant prostate cancer. Specifically, current therapies have limitations in that they are restricted to the post-chemotherapy setting; to date, an OS benefit in the chemotherapy-naïve setting has not been linked to objective response or impact on how a patient feels or functions; and chemotherapy has limited penetrance.2,3
Previous studies have shown that abiraterone acetate, an androgen biosynthesis inhibitor, improved OS in patients with metastatic castration-resistant prostate cancer who had previously progressed on docetaxel. Median survival was 14.8 months, an improvement of 3.9 months over the prednisone control arm.4
Dr. Ryan pointed out that landmarks of disease progression in metastatic castration-resistant prostate cancer occur over 24 to 48 months from a baseline diagnosis and encompass PSA progression, tumor/bone progression, chemotherapy, pain, ECOG PS decline, and death,5 and it is by having a positive effect on these landmarks that agents ideally would provide the most benefit.
The investigators of the phase 3 multicenter, randomized, double-blind, placebo-controlled study conducted at 151 sites in 12 countries in the USA, Europe, Australia, and Canada compared the clinical benefit of abiraterone acetate 1,000 mg/day plus prednisone 5 mg twice daily (n=546) vs placebo + prednisone 5mg twice daily (n=542) in chemo-naive, asymptomatic/mildly symptomatic patients with metastatic castration-resistant prostate cancer. Co-primary efficacy end points for the study were rPFS by central review and OS. Secondary end points were time to opiate use for cancer-related pain, time to initiation of chemotherapy, time to ECOG PS deterioration, and time to treatment progression. Patients were stratified by ECOG PS 0 or 1.
The definition of rPFS, adapted from consensus criteria,6 was progressive disease by bone scan by blinded central radiologist review (≥2 new bone lesions plus 2 additional at confirmation <12 weeks after randomization or ≥2 new bone lesions with subsequent confirmation ≥12 weeks after randomization) ; progressive disease in soft tissue lesions by CT or MRI by modified RECIST criteria; or death from any cause.