• Yoko Yamada, Nobuaki Matsubara, Tabata Ken-Ichi KI Department of Urology, Kitasato University School of Medicine, Sagamihara-shi, Kanagawa, Japan., Takefumi Satoh, Naoto Kamiya, Hiroyoshi Suzuki, Takashi Kawahara, Hiroji Uemura, Akihiro Yano, and Satoru Kawakami.
• Department of Breast and Medical Oncology, National Cancer Center Hospital East, 6-5-1 Kashiwanoha, Kashiwa, Chiba, 277-8577, Japan.
• BMC Res Notes. 2016 Oct 18; 9 (1): 471.

BackgroundBoth abiraterone acetate (AA) and enzalutamide are promising agents for patients with pre- and post-chemotherapy metastatic castration-resistant prostate cancer (mCRPC). Several retrospective analysis suggested clinical cross-resistance between these agents in patients previously treated with docetaxel. However, data on the antitumor activity of AA as a second androgen receptor-targeting new agent after the failure of enzalutamide in chemotherapy-naive mCRPC patients is unavailable.MethodsPatients with chemotherapy-naïve mCRPC who were treated with AA after disease progression with enzalutamide, were retrospectively reviewed at five institutions. Primary outcome measure was the rate of any prostate-specific antigen (PSA) decline. Secondary outcome measures were progression-free survival (PFS) and overall survival (OS) with subsequent AA treatment. We also performed correlation analysis between previous PSA response, PFS duration to enzalutamide and subsequent PSA response, PFS duration to AA.ResultsA total of 14 patients were identified. Any PSA declines and PSA decline ≥50 % with AA treatment, were observed in 36 and 7 % of patients, respectively. Median PFS with initial enzalutamide was 5.0 months (95 % CI 3.7-6.4 months), and for subsequent AA treatment was 3.4 months (95 % CI 0.8-6.0 months). Median OS from initiation of AA was 9.1 months (95 % CI 5.6-12.5 months). No significant correlations were observed between these PSA responses (Pearson r = -0.67, p = 0.82) and PFS duration (Kendall tau r = 0.33, p = 0.87).ConclusionsThe PSA decline with subsequent AA treatment in chemotherapy-naive mCRPC patients after a failure of enzalutamide was modest, however, the PFS and OS with subsequent AA treatment were comparable to those of enzalutamide previously reported as a second androgen receptor-targeting new agent after AA failure. The PSA response and PFS duration to previous enzalutamide treatment did not predict those of subsequent AA treatment.

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