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 CellSearch (R) System. Results: Higher CTC counts associated with baseline characteristics portending aggressive disease. Multivariate analyses indicated that a CTC >= 5 was an independent prognostic factor at all time points evaluated. Patients with baseline CTC >= 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 >= 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.