DETECTION OF MUTANT K-RAS DNA IN PLASMA OR SERUM OF PATIENTS WITH COLORECTAL-CANCER

Increased understanding of the molecular basis of colorectal cancer an d recognition that extracellular DNA circulates in the plasma and seru m of cancer patients enables new approaches to detection and monitorin g. We used a polymerase chain reaction (PCR) assay to demonstrate muta nt K-ras DNA in the plasma or serum of patients with colorectal cancer , Plasma or serum was fractionated from the blood of 31 patients with metastatic or unresected colorectal cancer and from 28 normal voluntee rs. DNA was extracted using either a sodium chloride or a gelatin prec ipitation method and then amplified in a two-stage PCR assay using sel ective restriction enzyme digestion to enrich for mutant K-ras DNA. Mu tant K-ras DNA was detected in the plasma or serum of 12 (39%) patient s, all confirmed by sequencing, but was not detected in any of the nor mal volunteers, K-ras mutations were detected in plasma or serum regar dless of sex, primary tumour location, principal site of metastasis or proximity of chemotherapy and surgery to blood sampling. Tumour speci mens available for 19 of the patients were additionally assayed for ra s mutations and compared with blood specimens. Our results indicate mu tant K-ras DNA is readily detectable by PCR in the plasma or serum of patients with advanced colorectal cancer, Thus, plasma-or serum-based nucleic acid amplification assays may provide a valuable method of mon itoring and potentially detecting colorectal cancer.