Background: In the phase 3 CHAARTED trial pts with mHSPC treated with ADT + D had an improved overall survival (OS) and longer time to castrate resistant prostate cancer (TTCRPC) than pts treated with ADT alone. We aimed to define the association of BTM levels with pt outcomes recognizing both ADT and bone metastases impact bone turnover. Methods: Serum samples were collected at baseline (BL) (within 28 days of starting ADT) in 233 (116 in ADT, 117 in ADT+D) pts and at week 24 in 423 (224 ADT+D, 199 ADT) pts. Samples were analyzed for osteocalcin (OC), osteoprotegrin (OPG), sclerostin (SL), RANKL and bone alkaline phosphatase (BALP). Cox proportional hazards models were used to assess the prognostic and predictive effects of the BTM in terms of OS and TTCPRC. Results: Whereas BALP baseline (BL) level < BL median was associated with longer OS independent of therapy (HR 0.44 95% CI 0.31-0.63, p<0.001); BL OPG > BL median and BL RANKL < BL median were associated with longer OS in the ADT+D arm (HR 0.54 95% CI 0.32-0.9, p=0.015 and HR 1.69 95% CI 1,03-2.79, p=0.037) but not in the ADT alone arm (HR 0.75, 95% CI 0.45 − 1.25, p=0.271 and HR 1.06 95% CI 0.65 − 1.73 p=0.827). Changes in markers from BL to week 24 varied based on treatment and volume of disease with statistically significant changes noted (Table). A rise in OC or BALP on therapy from BL to week 24 was associated with improved TTCRPC and OS (OC: HR(TTCRPC) 0.792, p=0.033, HR(OS) 0.78 p=0.047; BALP: HR(TTCRPC) 0.82, p=0.03, HR (OS) 0.79, p=0.013) controlling for week 24 levels. However higher absolute OC and BALP levels at week 24 were associated with worse outcomes. (OC: HR(TTCRPC) 1.37, p=0.003, HR(OS)1.38, p=0.006; BALP: HR(TTCRPC) 1.54, p=0.007, HR(OS) 1.77, p=0.001). Conclusions: The BL finding with BALP are consistent with higher BALP being a poor prognostic marker. The BL OPG and RANKL findings suggest these markers might identify men who benefit from addingf D to ADT. The paradoxical improved survival with a rise in OC and BALP on therapy but worse outcomes with absolute higher levels at week 24 highlights complex dynamics of bone turnover related to varied impact from ADT, bone healing when responding to therapy versus active cancer. Clinical trial information: NCT00309985.

LV=Low Volume; HV=High Volume.