Usefulness of circulating tumor cells after preliminary chemotherapy for prediction of response to further anticancer therapy in patients with initially unresectable metastatic colorectal cancer

The aim of this study was to evaluate the usefulness of circulating tumor cells (CTCs) after preliminary chemotherapy for prediction of response to further anticancer therapy in patients with initially unresectable metastatic colorectal cancer. CTCs from 14 consecutive patients with Kirsten rat sarcoma viral oncogene homolog (KRAS) wild-type colorectal cancer with synchronous or metachronous unresectable metastatic lesions were measured using the CellSearch system between January 2009 and December 2011. CTCs were measured before and after chemotherapy. The regimen consisted of four courses (three months) of oxaliplatin with oral S-1 (SOX) + panitumumab. Ten (71%) out of all patients had no detectable CTCs after chemotherapy. Eight out of these ten patients received further chemotherapy, and liver metastases were completely resected in the other two patients; none of these patients died of cancer within a year after starting chemotherapy. The remaining four patients with CTCs continued to have CTCs after chemotherapy, and all four of these patients died of cancer within eight months after starting chemotherapy. The prognosis of the patients who had no detectable CTCs after the chemotherapy was significantly better than that of those who had CTCs even after the chemotherapy (p