Predictors of resistance to abiraterone acetate or enzalutamide in patients with metastatic castration-resistant prostate cancer in post-docetaxel setting: a single-center cohort study

Treatment with abiraterone acetate or enzalutamide is one of the approved approaches in men with metastatic castration-resistant prostate cancer (mCRPC) in the post-docetaxel setting. However, a significant fraction of patients do not respond to treatment, and we aimed to determine their characteristics. From April 2015 to May 2019, 71 patients with mCRPC were treated with abiraterone acetate (N = 34) or enzalutamide (N = 37) at our institution. Resistance to treatment was defined as radiological or scintigraphic progression within 3 months, as documented at the first control. After a median follow-up of 14.9 months, resistance was detected in 22 patients (31%). Many of the baseline characteristics differed between responders and nonresponders but did not serve as predictors with clinically acceptable certainty. To overcome this, the resistance score was defined as the number of positive out of the following six predictors: (1) not only prostate specific antigen (PSA) progression after docetaxel (2) Eastern Cooperative Oncology Group (ECOG) performance status >1 (3) duration of metastatic disease (4) serum PSA >52 ng/mL (5) serum alkaline phosphatase >119 g/L (6) serum hemoglobin (Hb) concentration Most patients with resistance and a few responders had >3 positive predictors. Therefore, by using a cutoff of four positive predictors, the resistance score showed both a high sensitivity of 82% [57-96%; 95% confidence interval (CI)] and a specificity of 88% (74-96%; 95% CI). The proposed resistance score integrates the diagnostic performances of multiple predictors and may serve to decide which patients with mCRPC should be offered treatments other than hormonal therapy.