Durable Radiologic And Clinical Disease Stability Beyond Psa Progression In Patients With Metastatic Castration-Resistant Prostate Cancer (Mcrpc) Treated With Abiraterone Acetate (Aa)

4553 Background: AA, a potent oral CYP17A1 inhibitor is approved for treatment of mCRPC with a survival advantage of 4.9 months. In clinical practice, response evaluation remains challenging for pts with mCRPC. CTC conversion from CTC ≥ 5 to CTC u003c 5 with treatment predicts for improved overall survival in mCRPC. We hypothesized that pts continue to have durable disease stability beyond PSA progression on AA. Methods: Prostate Specific Antigen (PSA) responses, radiological responses and CTC conversion rates were retrospectively analysed in pts treated on AA at our institution. CTCs, PSA and imaging were obtained at predefined time points during these studies. Radiological and PSA progression were defined by standard Prostate Cancer Working Group Criteria II. Clinical progression consisted of worsening disease related pain, skeletal events or declining performance status.Pearson’s chi-squared test and the Kaplan-Meier method were used for this analysis. Results: 141 patients [ECOG Performance Status 0-2; Me...