Assessment of Total, PTEN–, and AR-V7+ Circulating Tumor Cell Count by Flow Cytometry in Patients with Metastatic Castration-Resistant Prostate Cancer Receiving Enzalutamide

Introduction. Metastatic castration-resistant prostate cancer (mCRPC) is a deadly disease. Enzalutamide is an oral second-generation anti-androgen that is active in mCRPC. Circulating tumor cells (CTC) count correlates with overall survival (OS) in mCRPC, whereas detection of the androgen-receptor splice variant 7 (AR-V7) in CTC predicts poor response to oral second-generation anti-androgens. Also, loss of PTEN (phosphatase and tensin homolog) in CTC is a biomarker of poor prognosis in mCRPC. Patients and methods. In this translational study, we employed flow cytometry to assess total, PTEN–, and AR-V7+ CTC count per 7.5 mL of whole blood in a prospective cohort of patients with mCRPC receiving enzalutamide. Results. CTCs were assessed in a total of 45 men with mCRPC at baseline and at 12 weeks. Overall, CTC, PTEN– CTC, and AR-V7+ CTC detection rate was high, at baseline, with 84.4%, 71.1%, and 51.1% of samples showing at least 1 cell/7.5-mL blood, respectively, and after 3 months, with 93.3%, 64.4%, and 77.7% of samples showing at least 1 cell/7.5-mL blood, respectively. Median radiographic progression-free survival (rPFS) and OS were 6 (95% confidence interval [CI], 5.6-9) and 14.3 (95% CI, 12.8-20.3) months, respectively. Median (interquartile range) total CTC count at baseline was 5 (3; 8), whereas median (interquartile range) PTEN– CTC count was 2 (0; 4) and median (interquartile range) AR-V7+ CTC count was 1 (0; 3). At baseline, ≥ 5 versus < 5 total CTC count was associated with worse rPFS (hazard ratio [HR], 2.35; 95% CI, 1.14-4.84; P=.021) and OS (HR, 3.08; 95% CI, 1.45-6.54; P =.003), whereas ≥ 2 versus < 2 PTEN– CTC count was associated with worse rPFS (HR, 3.96; 95% CI, 1.8-8.72; P=.001) and OS (HR, 2.36; 95% CI, 1.12-5; P=.025). Finally, ≥ 1 versus < 1 AR-V7+ CTC count was also associated with worse rPFS (HR, 5.05; 95% CI, 2.4-10.64; P