Circulating tumour cell (CTC) counts as intermediate end points in castration-resistant prostate cancer (CRPC): a single-centre experience.

BACKGROUND The purpose of this study was to evaluate the association of circulating tumour cell (CTC) counts, before and after commencing treatment, with overall survival (OS) in patients with castration-resistant prostate cancer (CRPC). EXPERIMENTAL DESIGN A 7.5 ml of blood was collected before and after treatment in 119 patients with CRPC. CTCs were enumerated using the CellSearchSystem. RESULTS Higher CTC counts associated with baseline characteristics portending aggressive disease. Multivariate analyses indicated that a CTC >or=5 was an independent prognostic factor at all time points evaluated. Patients with baseline CTC >or=5 had shorter OS than those with <5 [median OS 19.5 versus >30 months, hazard ratio (HR) 3.25, P=0.012]; patients with CTC >50 had a poorer OS than those with CTCs 5-50 (median OS 6.3 versus 21.1 months, HR 4.1, P<0.001). Patients whose CTC counts reduced from >or=5 at baseline to <5 following treatment had a better OS compared with those who did not. CTC counts showed a similar, but earlier and independent, ability to time to disease progression to predict OS. CONCLUSION CTC counts predict OS and provide independent prognostic information to time to disease progression; CTC dynamics following therapy need to be evaluated as an intermediate end point of outcome in randomised phase III trials.