To assess the use of circulating tumor cells (CTCs) as a longitudinal endpoint factor for clinical monitoring of patients with prostate cancer and to evaluate the association among the baseline CTC number, various clinical characteristics, and survival.

The CTCs were enumerated using the CellSearch Food and Drug Administration–cleared CTC kit in 202 patients with prostate cancer. Variables, including metastatic site, prostate-specific antigen level, Gleason score, testosterone level, and use of androgen treatment, were tested for association with the CTC number. The probability of patient survival over time was estimated using the Kaplan-Meier method.

The baseline CTC numbers were strongly associated with survival (P <.0001), with overall survival significantly poorer in patients with ≥5 CTCs. Significantly greater CTC numbers were observed in patients with bone metastasis (mean 41.12 CTCs) than in those with lymph node metastasis (mean 2.53 CTC, P = .026). Analysis of the association between the CTC count and prostate-specific antigen level revealed a weak positive correlation (correlation coefficient r = 0.2695, P = .0007). The CTC number also correlated with the Gleason score (P = .0138) and lower testosterone level (P <.0001). Patients without androgen depletion had significantly lower CTC numbers (mean 2.70) than those with androgen depletion (mean 26.39, P <.0001).

The baseline CTC counts were predictive of patient survival and correlated significantly with the clinical characteristics of patients with prostate cancer. Our study results have confirmed previous findings that support the use of CTC enumeration as a prognostic biomarker for patients with prostate cancer.