SWITCH: Study of the Prednisone to Dexamethasone Change in mCRPC Patients Treated With Abiraterone

This phase II multicentric-study analyse the role of the steroid switch in patients receiving AA. Previous retrospective data (Lorente et al, BJC 2014) has shown that the change of prednisone by dexamethasone in CRPC patients treated with AA post-docetaxel leaded to durable biochemical responses in 40% of cases. Recently, superiority of dexamethasone over prednisone in PSA response has been reported by a phase II trial that included 82 chemotherapy-naive metastatic CRPC patients. In our study patients with biochemical and/or limited radiological progression to AA + prednisone are prospectively enrolled. The principal objective was to evaluate the percentage of PSA responses in clinically stable metastatic CRPC patients after at least 12 weeks of AA + prednisone. Secondary aims will include time to biochemical progression, time to first radiological progression, overall survival and the evaluation of the safety profile. Biochemical response was monitored with PSA determinations every 4 weeks, and defined as a ≥ 30% decline in PSA from baseline, confirmed with a second reading. PSA progression was evaluated according to PCWG2 criteria. Radiological response was re-evaluated every 12-16 weeks using bone and CT-scan according to RECIST v1.1 and PCWG2 criteria. Translational studies: archival tissue will be obtained from all patients, to perform PTEN and TMPRSS-ERG rearrangements evaluation. Plasma will be collected after AA + prednisone progression to study the androgen receptor status in plasma.