842TiPPROSABI: Prospective multi-centre study of prognostic factors in castration resistant prostate cancer (CRPC) patients treated with abiraterone acetate (AA)

Background: The evolution of CRPC is heterogeneous, and despite progress in its management, with several new agents approved for CRPC, we are still so far from being able to predict which group of patients might benefit from a particular strategy. Therefore, the identification of new predictive and prognostic biomarkers is urgently needed. Trial design: PROSABI is a prospective multicentre observational study in metastatic CRPC designed to explore biomarkers in patients treated with AA. Key inclusion criteria: a) histological confirmation of prostate cancer; b) documented criteria (PCWG2) for CRPC; c) availability of tumour tissue; d) candidate for standard treatment with AA. Primary end point: to validate the prognostic value for overall survival (OS) of the expression signature (ES) in peripheral blood of 9 genes described by Olmos et al (Lancet Oncol 2012). Secondary end points: a) to study the prognostic role for progression-free survival of the ES; b) to analyse the prognostic role for OS of early changes in the ES; c) to compare the prognostic and predictive utility of the ES with other ES (Ross et al, Lancet Oncol 2012); d) to validate in this patient cohort prognostic nomograms described for CRPC. Exploratory outcomes: a) to establish prognostic value for TMPRSS-ERG and PTEN; b) to determine the prognostic value for serum testosterone levels; c) to analyse the role of serum chromogranine; d) to study the prognostic role of AR splicing variants; e) to explore new somatic and germinal variants in peripheral blood and tissue associated to dissemination, response and resistance to AA. PROSABI is part of the PROCURE Biomarkers network, a multicentric spanish platform for biomarkers discovery in CRPC patients. 220 patients will be accrued to provide appropriate statistical power to detect at least 91 events (deaths) to analyse the main outcome. Currently, 48 centres are active for recruitment and 184 patients have been included. Blood samples are collected before, during (pre-cycle 3) and after progression to AA. Prospective data collection will be linked. This study may help to incorporate new biomarkers in clinical practice and improve the selection of therapy in mCRPC. Clinical trial identification: NCT02787837 Legal entity responsible for the study: Spanish National Cancer Research Centre (CNIO) Funding: Spanish National Cancer Research Centre + grant from Janssen Disclosure: All authors have declared no conflicts of interest.