Detecting KRAS mutations in peripheral blood of colorectal cancer patients by peptide nucleic acid clamp PCR.

We investigated the effectiveness of peptide nucleic acid (PNA) clamp PCR for detecting KRAS mutations in peripheral blood samples of colorectal cancer (CRC) patients. We compared KRAS point mutations between tumour tissue and blood samples. Forty-two patients were included in this study. We observed KRAS mutations in formalin-fixed, paraffin-embedded tissues by PCR direct sequencing and in blood samples by PNA clamp PCR. KRAS point mutations were detected in primary tumour tissue samples of 13 patients (31.0%) and in peripheral blood samples of 10 patients (23.8%). KRAS point mutations were detected in both samples for 8 patients (19.0%). The sensitivity, specificity and accuracy for detecting KRAS mutations in peripheral blood and tumour tissue samples were 61.5, 93.1 and 83.3%, respectively. The positive and negative predictive values were 80.0 and 84.4%, respectively. Five patients with mutant KRAS in their plasma preoperatively, did not exhibit KRAS mutations postoperatively. Our method detected KRAS point mutations in peripheral blood samples of CRC patients, which contained extremely small amounts of mutant cells. This method is helpful for identifying metastatic CRC patients in whom metastases will respond to EGFR-targeted monoclonal antibody therapy.