Survival Outcomes, Prostate-specific Antigen Response, and Tolerance in First and Later Lines of Enzalutamide Treatment for Metastatic Castration-resistant Prostate Cancer: A Real-World Experience in Hong Kong

Abstract Background The present study retrospectively evaluated the efficacy and safety of enzalutamide in different lines of metastatic castration-resistant prostate cancer (mCRPC) treatment in a real-world setting. Patients and Methods The clinical records of patients with mCRPC treated with enzalutamide between August 2015 and October 2017 were retrieved from all 7 public oncology centers in Hong Kong and reviewed. The primary endpoint was progression-free survival (PFS) in first (1L), second (2L), and third or fourth lines (3L or 4L) of CRPC treatment. Secondary endpoints included overall survival (OS), prostate-specific antigen (PSA) response, and tolerance. Results Among a total of 117 patients (median age of 73 years [range, 52-90 years]), 34 (29.1%), 57 (48.7%), and 26 (19.3%) patients had enzalutamide as their 1L (chemo-naive), 2L (post-docetaxel or -abiraterone), and 3L or above treatment options. The overall PSA response rates were 43.6%, and were 73.5%, 35.1%, and 19.2% for 1L, 2L, and 3L or 4L treatment, respectively. PFS and OS were significantly associated with the line of treatment in the univariate survival analysis (1L/2L/3L and 4L; PFS, 7.1/3.9/2.2 months; OS, not reached/15.8/7.4 months; both P  = .0002) but not in the multivariate analysis. The observed incidence of any fatigue (grade 1 or 2, 54.7%; grade 3 or 4, 9.4%) was much higher than reported in the AFFIRM (A Study Evaluating the Efficacy and Safety of the Investigational Drug MDV3100 [ ClinicalTrials.gov Identifier: NCT00974311 ]) (any grade, 34%) and PREVAIL (A Multinational Phase 3, Randomized, Double-blind, Placebo-controlled Efficacy And Safety Study Of Oral Mdv3100 In Chemotherapy-naive Patients With Progressive Metastatic Prostate Cancer Who Have Failed Androgen Deprivation Therapy [ ClinicalTrials.gov Identifier: NCT00974311 ]) (any grade, 36%) trials; as well, grade ≥ 2 fatigue was significantly associated with 3L or 4L treatment ( P  = .01 in both univariate and multivariate analyses). Conclusion In the real-life setting, there was a higher incidence of enzalutamide-related fatigue than reported in the trials. Earlier lines of enzalutamide treatment were associated with longer PFS and OS, more frequent PSA response, and less fatigue.