Is there an antiandrogen withdrawal syndrome with enzalutamide?

Abstract

To examine prostate-specific antigen (PSA) levels after enzalutamide discontinuation to assess whether an antiandrogen withdrawal syndrome (AAWS) exists with enzalutamide. We retrospectively identified 30 consecutive patients with metastatic prostate cancer who were treated with enzalutamide after docetaxel. Post-discontinuation PSA results were available for all patients and were determined at 2-weekly intervals until starting further anticancer systemic therapy. PSA withdrawal response was defined as a PSA decline by ≥50% from the last on-treatment PSA, with a confirmed decrease ≥3 weeks later. Patient characteristics were evaluated in relation to the AAWS using univariate logistic regression analysis. The median (range) patient age was 70.5 (56-86) years and the median (range) follow-up was 9.0 (0.5-16) months. The most common metastatic sites were the bone (86.7%) and lymph nodes (66.7%). Most patients (70%) had previously received abiraterone and 12 patients (40%) had also received cabazitaxel. The median (range) treatment duration with enzalutamide was 3.68 (1.12-21.39) months. PSA levels after enzalutamide withdrawal were monitored for a median (range) time of 35 (10-120) days. Only one patient (3.3%) had a confirmed PSA response ≥50% after enzalutamide discontinuation. One patient (3.3%) had a confirmed PSA response of between 30 and 50% and another patient (3.3%) had an unconfirmed PSA response of between 30 and 50%. The median overall survival was 15.5 months (95% CI 8.1-24.7). None of the factors analysed in the univariate analysis were significant predictors of PSA decline after enzalutamide discontinuation. This retrospective study provides the first evidence that enzalutamide may have an AAWS in a minority of patients with metastatic castration-resistant prostate cancer. Further studies are needed to confirm the existence of an enzalutamide AAWS and to assess its relevance in prostate cancer management.