AR and metastatic prostate carcinoma: We examined 116 longitudinal CTC samples from a prospectively collected institutional cohort of 17 patients with metastatic prostate cancer, baseline samples from 2 phase II trials of the AR signaling inhibitors (ARSIs) enzalutamide and abiraterone with a total of 48 patients, and 217 longitudinal samples from 91 patients from a phase II trial of the ARSI seviteronel.