Background: Previous studies have indicated that ductal adenocarcinoma of the prostate (DA) is associated with adverse prognosis in patients with localized prostate cancer (PCa). However, the clinical significance of DA in advanced PCa remains largely ambiguous. This study endeavors to investigate the relationship between the existence of DA in prostate biopsy specimens and treatment outcomes among patients with advanced PCa receiving abiraterone acetate (AA) therapy. Methods: We retrospectively analyzed data from 440 patients with advanced PCa who received AA at either the metastatic hormone-sensitive (mHSPC, N=123) or castration-resistant PCa (mCRPC, N=317) stage. The presence of DA and its proportion was evaluated based on prostate biopsy specimens. Kaplan-Meier curves and COX regression were used to evaluate the predictive significance of DA on AA efficacy, including PSA response, PSA progression-free survival (PSA-PFS), and radiographic progression-free survival (rPFS). Results: In aggregate, DA was detected in 35/440 (8.0%) patients, with 13/440 (3.0%) and 22/440 (5.0%) men harboring DA<5% and ≥5%, respectively, in the total tumors. The overall PSA response rate in the entire cohort was 302/440 (68.6%), and it was comparable for people with and without DA, with both groups having a response rate of 68.6%. Of note, compared with patients without DA, men with DA have significantly longer median PSA-PFS (mPSA-PFS, 12.1- vs. 25.0-Mo, P=0.005) and median rPFS (mrPFS, 19.8 vs. 38.2-Mo, P=0.034). Subgroup analysis based on DA proportion further revealed that in comparison with PCa without DA, DA≥5% was an indicator of favorable PSA-PFS (HR, 95%CI: 0.28, 0.14-0.56, p<0.001) and rPFS (HR, 95%CI: 0.35, 0.18-0.72, p=0.004), while DA<5% was not. In multivariate COX regression analysis, after adjusting by clinicopathological factors, including mCRPC/mHSPC stage, ISUP grading, metastatic burden, pain score and pretreatment hemoglobin, alkaline phosphatase, and lactate dehydrogenase, DA≥5% was still independently associated with better therapeutic efficacy of AA treatment (PSA-PFS: HR, 95%CI: 0.36, 0.17-0.74, p<0.001; rPFS: HR, 95%CI: 0.47, 0.23-0.96, p=0.040). Conclusions: A DA proportion ≥5% in the tumor is related to improved treatment efficacy for individuals with advanced PCa receiving AA. Thus, in the pathological diagnosis of PCa, it is necessary to routinely report the presence and proportion of DA in order to aid with treatment decision-making.