Bone scan index as a biomarker to predict outcome in real-life mCRPC patients on abiraterone acetate: A multicenter study.

Abstract

217 Background: Bone Scan Index (BSI) is a quantitative measurement that reflects the tumor burden in bone calculated from bone scintigraphy. It also represents a prognostic marker in patients (pts) with metastatic castration resistant prostate cancer (mCRPC). Abiraterone acetate (AA) has showed to prolong survival before and after chemotherapy in this group of pts. In this study we evaluated the predictive value of BSI change as a biomarker of response in mCRPC patients on treatment with AA. Methods: We retrospectively studied 62 mCRPC pats who received AA following disease progression after chemotherapy at 3 different academic hospitals. Automated baseline and follow-up BSI data was obtained from images of whole-body bone scintigraphies performed before and during AA treatment. Data on clinical overall survival (OS), blood levels of prostate-specific antigen (PSA), alkaline phosphatase (ALP) and haemoglobin (Hb) at the time of baseline and upon follow-up was collected from medical records. The association between changes in these parameters at follow-up and survival was evaluated using Cox proportional-hazards regression models and Kaplan-Meier estimates of the survival function. Discrimination between prognostic variables was assessed using the concordance index (C-index). Results: Pts with an increase in BSI of > 0.3 (n=31) had 13% one year-survival rate compared to 42% for pts with improvement or stable disease according to BSI change at follow-up (BSI change < 0.3; n=31) (p< 0.001). Among all parameters evaluated (BSI, PSA, ALP, Hb) in a univariate Cox analysis, BSI change from baseline to follow-up presented the highest and strongest association with OS (C-index=0.7, Hazard ratio= 1.3 and p=0.0001). Conclusions: Increase in BSI of ≥ 0.3 is significantly associated with reduced survival in mCRPC pts under AA treatment following disease progression in a post-chemotherapy setting. BSI is a candidate biomarker to evaluate response and survival in this group, and change in BSI could be a valuable tool in monitoring pts with mCRPC on second-line therapies. BSI could then serve as a decision making tool supporting physicians to continue current treatment or to consider alternative therapies.