Circulating tumor cells (CTCs) are the most accurate and independent predictor of overall survival in patients with metastatic castration-resistant prostate cancer (CRPC), researchers have concluded.

Johann S. De Bono, MD, of Royal Marsden Hospital in Surrey, U.K., and colleagues based the finding on a study of 231 CRPC patients who had progressive disease and were starting a new line of chemotherapy. The patients had blood drawn before treatment and monthly thereafter. The investigators stratified the men into “favorable” or “unfavorable” groups (fewer than 5 and 5 or more CTC/7.5 mL, respectively).

Men with unfavorable pretreatment CTC counts had shorter overall survival compared with men who had favorable pretreatment CTC counts (median 11.5 vs. 21.7 months), the researchers reported in Clinical Cancer Research (2008;14:6302-6309). CTC counts predicted overall survival better than PSA levels.

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Overall survival of patients who converted from unfavorable baseline CTC to favorable CTC improved from a median of 6.8 months to 21.3 months; overall survival of patients who converted from favorable baseline CTC to unfavorable CTC decreased from a median of more than 26 months to 9.3 months.