Response to subsequent docetaxel in a patient cohort with metastatic castration-resistant prostate cancer after abiraterone acetate treatment

In this study, clinical outcomes after docetaxel therapy in 23 patients with metastatic castration-resistant prostate cancer (mCRPC) who progressed after treatment with abiraterone acetate (AA) were retrospectively evaluated. Subsequent docetaxel therapy led to ≥ 50% prostate-specific antigen (PSA) decline in 11 patients (48%) of patients; this outcome was not affected by pattern of AA resistance. The PSA response rates suggest that docetaxel and AA are not cross-resistant; however, further prospective study is required. Introduction/Background: Docetaxel or AA are therapeutic options for mCRPC. We retrospectively analyzed clinical outcomes with subsequent docetaxel in patients with mCRPC after disease progression (DP) with AA to evaluate cross resistance between these therapies. Patients and Methods: Patients with chemotherapy-naive mCRPC who were treated with AA in previously reported phase I to III trials, who had DP, and were subsequently treated (not on study) with docetaxel, were included. Acquired AA resistance was defined as: PSA decline > 50% from baseline or radiographically stable disease for 8 months, with subsequent DP. All other patients were defined as having primary AA resistance. Efficacy outcomes after docetaxel therapy were analyzed. Results: We identified 23 patients who were treated with docetaxel after DP with AA, including 14 (61%) with acquired and 9 (39%) with primary AA resistance. Median duration between discontinuation of AA and docetaxel initiation was 2.7 months (range, 0.2-14.7 months). Subsequent docetaxel therapy led to ≥ 30% PSA decline in 15 patients (65%) and ≥ 50% PSA decline in 11 patients (48%). Median OS from date of first docetaxel dose was 12.4 months (95% confidence interval, 8.2-19.6). Patients with previous primary versus acquired AA resistance had similar outcomes with subsequent docetaxel therapy. Conclusion: In this retrospective analysis, the type of AA resistance did not appear to affect outcomes with subsequent docetaxel. The PSA response rates observed suggest a lack of cross-resistance between docetaxel and AA, but prospective studies are needed to evaluate for potential cross-resistance and optimize sequences of therapy in patients with mCRPC.