To determine whether plasma circullating cell-free DNA (cfDNA) is a viable alternative approach for K-ras mutation testing in colorectal cancer (CRC) patients.

The study included 155 CRC patients. An a novel amplification refractory mutation system-based quantitative polymerase chain reaction with locked nucleic acid (LNA-ARMS-PCR) was developed to assess the K-ras mutation in preoperative plasma and paired tumor tissues. Firstly intra-tumoral heterogeneity analysis was used to determine whether it was a robust mutation detection method for the detection of low-abundance K-ras mutations.

The newly built LNA-ARMS-PCR was a robust mutation detection method to escape the most false negative caused by intra-tumoral heterogeneity. The positive consensus rate and negative consensus rate was 35.3% and 100.0%, between plasma and tumor tissue K-ras mutation detection, respectively. The majority of K-ras mutations detected in tumors were also found in plasma(15/18 (83.3%)) in patients of stage Ⅳ. The accordance of plasma and tumor mutation are strongly correlated to TNM stage and cfDNA level.

K-ras analysis in plasma cfDNA is only a viable alternative to tissue analysis in mCRC (stage Ⅳ). Quantitative levels of cfDNA and plasma mutation positivity are strongly correlated.

Colorectal cancer; K-ras; Locked nucleic acid; Amplification refractory mutation system