Exponential Rise in Prostate-Specific Antigen (PSA) during Anti-Androgen Withdrawal Predicts PSA Flare after Docetaxel Chemotherapy in Patients with Castration-Resistant Prostate Cancer

Purpose: To investigate the relationship between rising patterns of prostate-specific antigen (PSA) before chemotherapy and PSA flare during the early phase of chemotherapy in patients with castration-resistant prostate cancer (CRPC). Materials and Methods: This study included 55 patients with CRPC who received chemotherapy and in whom pre-treatment or post-treatment PSA levels could be serially obtained. The baseline parameters included age, performance, Gleason score, PSA level, and disease extent. PSA doubling time was calculated using the different intervals: the conventional interval from the second hormone manipulation following the nadir until anti-androgen withdrawal (PSADT1), the interval from the initial rise after anti-androgen withdrawal to the start of chemotherapy (PSADT2), and the interval from the nadir until the start of chemotherapy (PSADT3). The PSA growth patterns were analyzed using the ratio of PSADT2 to PSADT1. Results: There were two growth patterns of PSA doubling time: 22 patients (40.0%) had a steady pattern with a more prolonged PSADT2 than PSADT1, while 33 (60.0%) had an accelerating pattern with a shorter PSADT2 than PSADT1. During three cycles of chemotherapy, PSA flare occurred in 11 patients (20.0%); of these patients, 3 were among 33 (9.1%) patients with an accelerating PSA growth pattern and 8 were among 22 patients (36.4%) with a steady PSA growth pattern (p=0.019). Multivariate analysis showed that only PSA growth pattern was an independent predictor of PSA flare (p=0.034). Conclusion: An exponential rise in PSA during anti-androgen withdrawal is a significant predictor for PSA flare during chemotherapy in CRPC patients.