Objective To determine the influence of abiraterone acetate (AA) on neuroendocrine differentiation (NED) in metastatic castration-resistant prostate cancer (mCRPC) and the prognostic predicting value of the serum NED markers in mCRPC patients treated with AA.Methods We conducted an analysis in 115 chemotherapy-naive mCRPC patients who were treated with chemotherapy in Renji hospital from 2013 to 2017.The median age was 70,ranged from 65 to 76 years old.The median CgA,NSE and PSA levels were 101.1 ng/ml (78.5-150.0 ng/ml),13.4 ng/ml (10.5-17.6 ng/ml) and 38.8 ng/ml (11.2-123.2 ng/ml),respectively.Among them,48 cases were classified as the group without AA treatment.The other 67 cases were classified as group after AA failure.In group without AA treatment,the median CgA,NSE and PSA levels were 109.1 ng/ml(80-151.5 ng/ml);13.8 ng/ml(10.8-18.2 ng/ml) and 39.2 ng/ml (8.6-200 ng/ml),respectively.In group after AA failure,the median CgA,NSE and PSA levels were 105.4 ng/ml(78.8-175.5 ng/ml),13.8 ng/ml(10.8-17.6 ng/ml) and 39.0 ng/ml(8.4-219.8 ng/ml),respectively.In the group with serial evaluation of NED markers during AA treatment,the median serum CgA,NSE levels at baseline were 115.9 ng/ml(90.1-201.5 ng/ml),13.3 ng/ml (10.4-18.1 ng/ml),respectively.The endpoints were PSA PFS(progression-free survival) and radiographic PFS (rPFS).Results In 34 patients with serial evaluation,serum NED markers level in 19 patients increased after the failure of AA treatment.Median serum CgA and NSE levels were 115.9 ng/ml(90.1-201.5 ng/ml)and 13.25 ng/ml (10.37-18.14 ng/ml) at baseline.Median serum CgA and NSE levels were 129.6ng/ml (75.5-230.5 ng/ml) and 14.7 ng/ml (11.8-19.1 ng/ml) after 6 months treatment,respectively.The median serum CgA and NSE levels were 130.4 ng/ml (95.7-205.7 ng/ml) and 15.2 ng/ml(12.4-18.7 ng/ml) at the time of failure of AA treatment,respectively.There was no significant difference of NED markers between baseline and failure of AA treatment (P =0.243).In logistic univariate analysis,AA treatment and its duration were not independent factors influencing NED(P =0.30;P =0.52).Compared with the NED markers elevation group in the first 6 months of AA treatment and baseline supranormal NED markers group,the NED markers decline group(PSA PFS(17.1 vs.10.4 months,P ＜ 0.001) and rPFS (17.0 vs.10.4 months,P =0.003)) and baseline normal NED markers group(PSA PFS(14.1 vs.9.5 months,P =0.001) and rPFS(16.4 vs.10.5 months,P ＜ 0.001)) has a longer median PSA PFS and rPFS respectively.In multivariate Cox analysis,baseline NED markers level and NED markers variation during the first 6 months of AA treatment remained significant predictors of rPFS(P ＜ 0.05),and PSA-PFS (P ＜ 0.05).Conclusions We found there was heterogeneity in changes of NED markers in different mCRPC patients during AA treatment,and AA might not significantly lead to progression of NED of mCRPC in general.Serial CgA and NSE evaluation might help clinicians guide clinical treatment of mCRPC patients.Serum NED markers elevation during the first 6 months of AA treatment and elevated baseline NED markers levels indicated poor prognosis in mCRPC treated with AA.