OBJECTIVETo detect RAS mutations in the circulating cell-free DNA (cfDNA) in the plasma and explore the their correlation with the clinicopathological features in patients with colorectal cancer.

METHODSReal-time PCR was used to detect RAS mutations in plasma cfDNA and matched tumor tissue DNA samples from 71 colorectal cancer patients. The correlation of RAS mutations with the clinicopathological features of the patients were analyzed.

RESULTSOf the 71 patients with colorectal cancer, 23 (32.39%) showed RAS mutations in the cfDNA and 36 (50.7%) showed RAS mutations in tumor tissue DNA, with a concordance rate of 76.06% in the results between the two samples (Kappa=0.523). RAS mutations in the cfDNA were not related to the patients' age (P=0.072), gender (P=0.320), tumor stage (IVa and IVb, P=0.450), primary tumor position (P=0.324), lung metastasis (P=0.237), CEA level (P=0.284) or CA199 level (P=0.427). The positivity rate of RAS mutations in plasma cfDNA was significantly higher in patients with liver metastasis than those without liver metastasis (P=0.045).

CONCLUSIONPlasma cfDNA can be a reliable source of diagnostic DNA to replace the tumor tissue DNA for diagnosis of RAS mutations. RAS mutations in plasma cfDNA occur more frequently in colorectal cancer patients with liver metastasis.