Increase in bone scan index during abiraterone treatment in relation to reduced survival in mCRPC patients.

Abstract

244 Background: Abiraterone acetate (AA) is one of several new treatment options for patients with metastatic castration-resistant prostate cancer (mCRPC). It has showed to prolong survival in patients who had disease progression after chemotherapy. An objective biomarker that is associated with improvement in survival would be of value in the management of patients under AA treatment, for example in decisions to continue or change treatment. Bone Scan Index (BSI) is a measurement that reflects the tumor burden in bone as a percent of the total skeletal mass. The purpose of this study was to evaluate BSI as a response biomarker in mCRPC patients on treatment with AA. Methods: We retrospectively studied a consecutive series of 28 mCRPC patients who received AA following disease progression after chemotherapy. All patients had undergone whole-body bone scan before and during AA treatment. Baseline and follow-up BSI data was obtained using the automated quantification software EXINI Bonebsi(EXINI Diagnostics AB, Sweden). Data on prostate-specific antigen (PSA) and survival were collected from the medical records. Cox proportional-hazards regression models and Kaplan-Meier estimates of the survival function were used to investigate the association between changes in BSI and PSA from baseline to follow-up and survival. Discrimination between prognostic variables was assessed using the concordance index (C-index). Results: Patients with an increase in BSI of at least 0.2 (n=15) had a worse one-year survival (36%) than those with improvement or stable disease (BSI change <0.2) (96%) (p< 0.006). Both follow-up BSI and the BSI change from baseline to follow-up showed higher C-index (0.80) than the corresponding PSA values (0.73 and 0.75). Conclusions: Increase in BSI is significantly associated with reduced survival in mCRPC patients under AA treatment following disease progression after chemotherapy. Calculation of BSI could be a valuable tool for treatment response evaluation as a complement to the traditional methods. [Table: see text]