Sofia España,1 Maria Ochoa de Olza,2 Nuria Sala,3 Josep Maria Piulats,2 Ulises Ferrandiz,1 Olatz Etxaniz,1 Lucia Heras,2,4 Oscar Buisan,5 Juan Carlos Pardo,1 Jose F Suarez,6 Pilar Barretina,3 Josep Comet,7 Xavier Garcia del Muro,2 Lauro Sumoy,8 Albert Font1 1Catalan Institute of Oncology, Medical Oncology Department, University Hospital Germans Trias I Pujol, Badalona, Spain; 2Catalan Institute of Oncology, Medical Oncology Department, Bellvitge University Hospital, Hospitalet De Llobregat, Spain; 3Catalan Institute of Oncology, Medical Oncology Department, University Hospital Josep Trueta, Girona, Spain; 4Medical Oncology Department, Hospital Sant Joan Despí Moisès Broggi, Barcelona, Spain; 5Urology Department, University Hospital Germans Trias I Pujol, Badalona, Spain; 6Urology Department, Bellvitge University Hospital, Hospitalet de LLobregat, Spain; 7Urology Department, University Hospital Josep Trueta, Girona, Spain; 8High Content Genomics & Bioinformatics Unit, Germans Trias I Pujol Research Institute (IGTP), Program of Predictive and Personalized Medicine of Cancer (PMPPC), Campus Can Ruti, Badalona, SpainCorrespondence: Albert FontCatalan Institute of Oncology, Medical Oncology Department, University Hospital Germans Trias I Pujol, Ctra Canyet, s/n, Badalona 08916, SpainEmail afont@iconcologia.netBackground: Abiraterone acetate (AA) is widely used in the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC). However, a significant percentage of patients will still progress, highlighting the need to identify patients more likely to benefit from AA. Parameters linked to prostate-specific antigen (PSA) kinetics are promising prognostic markers. We have examined clinical and PSA-related factors potentially associated with overall survival (OS) in patients treated with AA.Methods: Between 2011 and 2014, 104 patients with mCRPC treated with AA after progression to docetaxel at centers of the Catalan Institute of Oncology were included in this retrospective study. Patients were assessed monthly. Baseline characteristics and variables related to PSA kinetics were included in univariate and multivariate analyses of OS.Results: Median OS was 16.4 months (range 12.4– 20.6) for all patients. The univariate analysis identified the following baseline characteristics as significantly associated with OS: ECOG PS, location of metastases, time between starting androgen deprivation therapy and starting AA, time between stopping docetaxel treatment and starting AA, neutrophil-lymphocyte ratio (NLR), alkaline phosphatase levels, and PSA levels. Factors related to PSA kinetics associated with longer OS were PSA response > 50%, early PSA response (> 30% decline at four weeks), PSA decline > 50% at week 12, PSA nadir < 2.4ng/mL, time to PSA nadir > 140 days, the combination of PSA nadir and time to PSA nadir, and low end-of-treatment PSA levels. The multivariate analysis identified ECOG PS (HR 37.46; p< 0.001), NLR (HR 3.7; p< 0.001), early PSA response (HR 1.22; p=0.002), and time to PSA nadir (HR 0.39; p=0.002) as independent prognostic markers.Conclusion: Our results indicate an association between PSA kinetics, especially early PSA response, and outcome to AA after progression to docetaxel. Taken together with other factors, lack of an early PSA response could identify patients who are unlikely to benefit from AA and who could be closely monitored with a view to offering alternative therapies.Keywords: castration-resistant prostate cancer, abiraterone, PSA kinetics, survival, early PSA response