Impact of circulating tumor cell (CTC) nucleus size on outcomes with abiraterone acetate (AA) therapy in men with metastatic castration-resistant prostate cancer (mCRPC).

253Background: CTC enumeration but not CTC morphology has been reported to predict outcomes to treatment in men with mCRPC. Recently Chen JF et. al (Cancer, 2015) showed an association with nuclear size and incidence of visceral disease in metastatic prostate cancer. In this study, we investigate the impact of CTC nucleus size on outcomes in men treated with AA for mCRPC. Methods: In a cohort of men with mCRPC treated with first-line AA, who had CTCs identified by CellSearch (CS) analysis prior to initiating treatment, we retrospectively quantified the nuclear size of CTCs by ImageJ/Fiji 1.46 software and correlated with progression free survival (PFS) on AA. We analyzed with univariate in addition to pre-specified multivariable analysis adjusted for Gleason score and baseline log PSA to assess independent predictive value of CTC nuclear size on PFS. Median PFS was calculated by Kaplan-Meier analysis and p-values were determined from Cox proportional hazards model. Results: 22 men treated with AA for mCRP...