K-RAS MUTATIONS ARE FOUND IN DNA EXTRACTED FROM THE PLASMA OF PATIENTS WITH COLORECTAL-CANCER

Background & Aims: Circulating DNA can be isolated from the plasma of healthy subjects and from patients with cancer. The aim of this study was to detect K-ras mutations in DNA extracted from the plasma of pati ents with colorectal cancer. Methods: Tumor and plasma DNA were extrac ted from 14 patients with colorectal cancer (stages A-D), and K-ras al terations were detected using a polymerase chain reaction assay that u ses sequence-specific primers to amplify mutant DNA. These results wer e confirmed with another polymerase chain reaction assay that creates an enzyme restriction site in the absence of a K-ras mutation followed by direct sequencing and additional cloning techniques. Results: Seve n patients (50%) had a codon 12 K-ras mutation within their primary tu mor, and identical mutations were found in the plasma DNA of 6 patient s (86%). Mutant DNA was not detected in the plasma specimens of 7 pati ents whose tumors tested negative for K-ras alterations or in healthy control subjects. Similar results were obtained using all three molecu lar biological techniques. Conclusions: K-ras abnormalities can be det ected in circulating DNA extracted from the plasma specimens of patien ts with colorectal cancer. If these results are confirmed in larger st udies, genetic analysis of plasma DNA may have clinical applications i n the future.