Potential Value of Rapid Prostate-Specific Antigen Decline in Identifying Primary Resistance to Abiraterone Acetate and Enzalutamide

AIM: To identify factors predicting primary resistance to new-generation hormonal agents (NHAs), abiraterone acetate and enzalutamide in patients with castration-resistant prostate cancer (CRPC). PATIENTS & METHODS: Our hospital has conducted two successive named patient NHA programs. A total of 57 patients with progressive CRPC previously treated with first-line docetaxel-based chemotherapy received standard NHA doses: abiraterone acetate 1000 mg once-daily combined with prednisone (5 mg twice daily) or enzalutamide 160 mg once-daily. Patients, who were assessed monthly to check their hematological parameters and prostate-specific antigen (PSA) levels, also underwent imaging investigations every 3-4 months. In total, 24 variables were assessed as potential predictors of primary NHA resistance. RESULTS: Univariate analysis indicated that baseline pain and lactate dehydrogenase levels, and PSA levels after 1 month's treatment were predictive of primary NHA resistance. Only the predictive value of PSA levels after 1 month of treatment was confirmed at multivariate analysis. This factor strongly predicted progression-free and overall survival. CONCLUSION: RESULTS suggest the use of a simple and rapid method of identifying patients with primary resistance to NHAs: patients not achieving a ≥ 50% reduction in PSA levels within the first treatment month should undergo intensive investigations to verify whether they have primary resistance to NHAs.