Enzalutamide after failure of docetaxel and abiraterone in metastatic castrate resistant prostate cancer (mCRPC): Results from an expanded access program.

Abstract

188 Background: Abiraterone or enzalutamide are licensed for use post-docetaxel in metastatic castrate resistant prostate cancer (mCRPC). Both target the androgen receptor signalling pathway. There is little information describing their sequential use. Methods: Patients with mCRPC who had failed treatment with docetaxel and abiraterone received enzalutamide as part of an expanded access program. Patients were reviewed four weekly and post-treatment PSA used to determine efficacy. Results: Twenty three patients, median age 76 (range, 65 to 82), performance status of 1 (15/23) or 2 (8/23) with mCRPC (22/23 bone and 4/23 visceral disease) were enrolled. All had received prior docetaxel and abiraterone as well as cabazitaxel (35%), dexamethasone (30%), and stillboestrol (52%). Median biochemical progression free survival (bPFS) was 11.9 weeks. Nine (39%) patients showed sensitivity to enzalutamide, defined as a greater than 50% reduction in PSA. There was a correlation between PSA response to abiraterone and enzalutamide (R=0.45, p=0.03). In 10 out of 23 and 13 out of 23 patients who were sensitive and insensitive to abiraterone, 60% and 23% had a great than 50% reduction in PSA, respectively. There was a trend to improved bPFS in those sensitive to abiraterone (15.7 vs. 11.4 weeks, p=0.40) and in those who showed any PSA response to abiraterone (15.9 vs. 5.3 weeks, p=0.06). Conclusions: Enzalutamide has activity following failure of docetaxel and abiraterone in mCRPC. The effectiveness is more pronounced in those who have responded to abiraterone.