Correlation of circulating tumor cells (CTCs) and clinical biomarker endpoints in metastatic prostate cancer patients.

e15124 Background: Circulating tumor cells (CTCs) are found in human blood when cancers undergo metastatic dissemination, and CTCs have been reported as a surrogate marker for tumor response and linked to shorter survival in metastatic prostate cancer patients. This study assessed the use of CTCs as a continuous factor for clinical monitoring of prostate cancers patient in real time and evaluated the association between baseline CTC number, various clinical characteristics, and survival. Methods: CTCs were enumerated using the CellSearch FDA cleared CTC kit in 206 patients with metastatic prostate cancer. Variables including metastatic site, PSA, Gleason score, level of testosterone and androgen treatment were tested for association with CTC number. The probability of patient survival over time was estimated by the Kaplan-Meier method. Results: Baseline CTC numbers were strongly associated with survival (p<0.0001), with overall survival being significantly poorer in patients with ≥5 CTCs. Significantly higher CTC numbers were observed in patients with bone metastasis (mean=41.1 CTCs) compared to those with lymph node metastasis (mean=2.5 CTC, p=0.026). Analysis of the association between CTC counts and PSA level revealed a weak positive correlation between CTC number and PSA (Correlation coefficient r=0.269, Significance level p<0.001). CTC number further correlated with the Gleason score (p=0.009) and lower testosterone levels (p<0.0001). Patients with no androgen depletion had significantly lower numbers of CTCs (median=3.94) compared to those with androgen depletion (median=406, p<0.001). Conclusions: Baseline CTCs are predictive of patient survival and are significantly correlated with clinical characteristics in prostate cancer patients.Our study confirms previous findings that support the use of CTC levels as a prognostic biomarker for prostate cancer patients.