Prospective Evaluation Of The Response To Prednisone-Dexamethasone Switch In Castration-Resistant Prostate Cancer Patients Treated With Abiraterone Pre- And Post-Docetaxel.

327 Background: Abiraterone acetate (AA) administered with prednisone (P) to reduce mineralocorticoid-related adverse events improves survival in CRPC with a favourable tolerance profile. However, in the phase I/II of AA without steroids, dexamethasone 0,5mg/day was added after biochemical progression reaching a 25% of PSA decline. Lorente et al (BJC, 2014) showed durable biochemical responses in 40% of cases treated with AA and steroid switch in the post-docetaxel setting. We hypothesize that P to D switch in patients with biochemical progression to AA+P would lead to secondary responses also in the pre-docetaxel setting. Methods: Change of P 5mg/12h to D 0.5mg/24h was prospectively tested in clinically stable CRPC with biochemical progression ( u003e 25% PSA rise over nadir, confirmed in a second determination) and/or limited radiological progression ( u003c 3 new bone/lymphatic metastasis, non-bulky), after ³12 weeks of AA+P. PSA was monitored q4wks. CT- u0026 bone-scans were performed every 12-16 weeks. Biochemic...