Circulating tumor cells as a surrogate marker for determining response to chemotherapy in Japanese patients with metastatic colorectal cancer.

The purpose of this study was to investigate the potential of circulating tumor cells (CTC) as a surrogate marker of the clinical outcome in metastatic colorectal cancer (mCRC) patients in order to identify Japanese patients responsive to oxaliplatin-based chemotherapy. Between January 2007 and April 2008, 64 patients with mCRC were enrolled in this prospective study. The treatment regimen was oxaliplatin-based chemotherapy. Collection of CTC from whole blood was performed at baseline and at 2 and 8-12 weeks after initiation of chemotherapy. Isolation and enumeration of CTC was performed using immunomagnetics. Patients with ≥3 CTC at baseline and at 2 and 8-12 weeks had a shorter median progression-free survival (8.5, 7.3 and 1.9 months, respectively) than those with <3 CTC (9.7, 10.4 and 9.1 months, respectively) (log-rank test: P = 0.047, P < 0.001 and P < 0.001, respectively). Patients with ≥3 CTC at 2 and 8-12 weeks had a shorter median overall survival (10.2 and 4.1 months, respectively) than those with <3 CTC (29.1 and 29.1 months, respectively) (P < 0.001 and P = 0.001, respectively). A spurious early rise in carcinoembryonic antigen level was observed in 11 patients showing a partial response. In contrast, no rise in early CTC level was observed among responders. Our data support the clinical utility of CTC enumeration in improving our ability to accurately assess treatment benefit and in expediting the identification of effective treatment regimens for individual Japanese patients.