334 Background: Under early Enzalutamide (Enza) treatment of bone mCRPC (bmCRPC), prostate-specific antigen (PSA) might be misleading, since a PSA-flare may occur. Bouncing of alkaline phosphatase (APB) was shown as a promising surrogate for survival outcome. Low lactate dehydrogenase (LDH) usually predicts better outcome. The purpose of this study was to evaluate the prognostic ability of APB, LDH, PSA and information of the pooled markers after initiation of Enza. Methods: 89 bmCRPC-patients were analyzed. PSA, LDH and AP were monitored at 2, 4, 8, 12 and 20 weeks. APB was defined as an increase of AP after initiation of Enza with a subsequent, significant decline below baseline during the first 8 weeks of therapy. APB vs. no Bounce as well as LDH and PSA increase vs. decline were analyzed using Kaplan-Meier analyses (KMA) and uni- and multivariate (UV/MV) cox-regression models. Results: In KMA declining PSA and LDH as well as APB were associated with longer median PFS with 7 (95% confidence interval: 4.2-9.8) vs. 3 months (2.3-3.7) for PSA, 6 (4.1-8) vs. 2 (1.2-2.8) for LDH and 8 (0-16.3) vs. 3 (1.9-4.1) for APB. Analysis of OS showed similar results with 17 (11.7-22.3) vs. 12 months (7.0-17.1) for PSA, 17 (13.2-20.8) vs. 7 (5,8-8.2) for LDH and 19 (7.9-30.1) vs. 12 (7.7-16.3) for APB. In UV APB (Hazard Ratio (HR): 0.52 (0.3-1.0); p = 0.02), PSA-decline ≥50% (HR: 0.49 (0.3-0.7); p < 0.01) and LDH-normalization (LDHnorm) (HR: 0.39 (0.2-0.6); p < 0.01) were significantly associated with longer PFS. Considering OS LDHnorm was a significant prognosticator for longer survival (HR: 0.39 (0.2-0.6); p < 0.01). In MV only LDHnorm showed a trend towards better OS (HR: 0.49 (0.2.-1.1); p = 0.09). Combining those markers and separating a group with APB, LDHnorm and PSA-decline and a group with PSA-decline alone KMA showed better PFS (11 (0.2-21.8) vs. 4 (0-8.6)) and OS (20 (17.7-22.3) vs. 8 (0.3-15.7)) in favor of the group with 3 beneficial markers. In UV the presence of all 3 markers was significantly associated with longer PFS (HR: 0.23 (0.1-0.7); p < 0.01) and OS (HR: 0.26 (0.1-0.8); p = 0.02). Conclusions: APB and LDHnorm may add to identifying bmCRPC-patients with favorable prognosis during early Enza-therapy.