K ras mutation detection using a novel amplification refractory mutation system based quantitative polymerase chain reaction with locked nucleic acid blocker in plasma among colorectal cancer patients
Objective To determine whether plasma circullating cell free DNA (cfDNA) is a viable alternative approach for K ras mutation testing in colorectal cancer (CRC) patients. Methods 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. Results 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. Conclusion 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. Key words: Colorectal cancer; K ras; Locked nucleic acid; Amplification refractory mutation system