Abstract
e16514 Background: Abiraterone acetate (AA) prolongs survival in men with mCRPC in the pre- and post chemotherapy setting and is mainly used in asymptomatic men. In the first 12 weeks an early rise of prostate specific antigen (PSA) may occur followed by either delayed decline (PSA-flare) or true progression. Bouncing of alkaline phosphatase (ALP-Bouncing) was shown to be a promising marker for outcome and response during very early AA therapy. This retrospective study was conducted to analyze the capability of ALP-Bouncing to predict overall survival (OS) in men with bone mCRPC (bmCRPC) with rising PSA after initiation of AA therapy. Methods: Men with bmCRPC and rising PSA during early AA therapy were includeded and analyzed. PSA response rate (RR) was monitored according to PCWG2 criteria and assessed 12 weeks after start of AA treatment. PSA-flare vs. no flare and ALP-Bouncing vs. no Bouncing were analyzed using Kaplan-Meyer estimates and uni- and multivariate (UV/MV) cox-regression models. ALP-Bouncing was defined as increase of ALP after the beginning of AA with a subsequent significant decline below baseline during the first 8 weeks of therapy. Results: Forty men were evaluable for analysis: 20 men were chemotherapy naïve, 20 pretreated with docetaxel. The PSA RR was 30%. The median survival for ALP-Bouncing was 20 months (95% confidence interval (95%CI): 4.7-13.3) vs. 9 months (95%CI not distinguishable) for no ALP-bouncing (p = 0.04) and 13 months (95%CI: 8.8-17.2) for PSA-flare vs. 9 months (95%CI 4.4-13-6) for no PSA-flare (p = 0.62). In UV no ALP-bouncing was significantly associated with worse OS (Hazard Ratio (HR): 2.65 (95%CI: 1.0-7.0); p = 0.05). After adjustment for PSA-flare no AP-bouncing remained an independent prognosticator of worse OS (HR: 2.78 (95%CI: 1.0-7.71); p = 0.05). Conclusions: ALP-Bouncing, occurring earlier than delayed PSA-decline, may be a helpful marker to identify patients with subsequent favorable outcome in men with bmCRPC and rising PSA after initiation of AA therapy. These results have to be validated in a prospective trial.
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