1394P Alkaline phosphatase (ALP) decline and pain response as markers for overall survival (OS) in patients (Pts) with metastatic castration-resistant prostate cancer (mCRPC) treated with radium-223 (223Ra) in the REASSURE study

223Ra prolongs OS in pts with bone-predominant mCRPC. Here, we evaluated potential associations of ALP decline and pain response with OS during 223Ra treatment in the global, real-world REASSURE study, with the aim to define patient subgroups with different survival outcomes, which may help improve disease management strategies. Pts treated with 223Ra were grouped by any ALP decline vs no decline and pain response vs no response, based on ALP levels at baseline (BL) and week 12 and the best pain response during 223Ra treatment. Pain levels were assessed using the Brief Pain Inventory-Short Form (BPI-SF). Cox proportional hazard models with 95% confidence intervals (CIs) were provided for associations between ALP decline and pain response with OS. Data were from 779 pts with ALP measurements at both BL and week 12. In total, 624 (80%) pts had a decline in ALP and 155 (20%) had no decline (Table). Pts with ALP decline had longer OS than pts with no decline (HR 0.739, 95% CI 0.601–0.916). For pts who had pain at BL (BPI-SF of ≥2) and ALP decline, OS was similar regardless of pain response (Table). In contrast, for pts with pain at BL and no ALP decline, OS was longer in pts with pain response than without (HR 0.498, 95% CI 0.322–0.768). For pts who had no pain at BL (BPI-SF of 0 or 1), OS was longer in pts who had ALP decline compared with those without (HR 0.581, 95% CI 0.354–1.007).Table: 1394PVariablesPatients (N)Median OS (m) (95% CI)HR (95% CI)Any ALP decline vsNo ALP decline*62415518.1 (17.0-19.5)14.2 (12.3-16.4)0.739 (0.601-0.916)Any ALP decline* and BL BPI-SF ≥2Pain response vsNo pain response27914917.8 (16.3-19.5)17.0 (13.8-19.3)0.915 (0.717-1.173)No ALP decline* and BL BPI-SF ≥2Pain response vsNo pain response625316.2 (13.5-19.7)10.9 (8.3, 14.7)0.498 (0.322-0.768)No pain at BL (BPI-SF 0 or 1)Any ALP decline vsNo ALP decline*1342822.4 (18.9-26.7)20.3 (10.5-26.5)0.581 (0.354-1.007)*Measured at week 12BL, baseline; BPI-SF, Brief Pain Inventory-Short Form; CI, confidence interval; HR, hazard ratio; m, months; N, number; OS, overall survival Open table in a new tab *Measured at week 12 BL, baseline; BPI-SF, Brief Pain Inventory-Short Form; CI, confidence interval; HR, hazard ratio; m, months; N, number; OS, overall survival ALP decline after 12 weeks of 223Ra treatment was associated with longer survival. In pts without ALP decline, pain response was associated with longer OS, compared with those without a pain response. The shortest OS was observed in pts with baseline pain, no ALP decline and no pain response, whilst the longest OS was seen for pts who had no pain at BL and had ALP decline.