Measuring circulating tumor cells (CTCs) may be a more effective method of predicting survival compared with PSA tests in patients with metastatic castration-resistant prostate cancer (CRPC), according to a study published online ahead of print in the Journal of Clinical Oncology.

The study, which was conducted by Amir Goldkorn, MD, and colleagues at the Keck School of Medicine of the University of Southern California in Los Angeles, looked at blood samples of 263 men with metastatic CRPC prior to chemotherapy. They enumerated CTCs at baseline and three weeks after treatment in 263 men.

At baseline, subjects had a median CTC count of 5 cells per 7.5 mL. The median overall survival (OS) was 26 months for men with fewer than 5 CTCs per 7.5 mL versus 13 months for those with 5 or more CTCs per 7.5 mL at baseline, which translated into a 2.7 times increased risk of death for those with 5 or more CTCs per 7.5 mL.

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Patients who had elevated CTC after chemotherapy had up to a 5-fold increased risk of death, whereas patients whose CTC counts dropped by 50% or more were half as likely to die.

The authors said they believe that this method can help to prevent harmful and unnecessary testing in men who are eligible of undergoing PSA screening.

The significance of these findings is that CTC counts before and 3 weeks after the first cycle of chemotherapy are an early indicator of whether these patients would do well with treatment and how long they may live, Dr. Goldkorn noted. “This could help guide clinicians’ treatment decisions and save patients from toxic treatment that won’t help them.”

The researchers plan to follow-up on this study by molecularly analyzing CTC counts in order to figure out what genes and mutations they possess that allows them to be an effective biomarker.