Detection of Tumor DNA in Serum of Colorectal Cancer Patients

We previously found p16 promoter methylation in DNA in the sera of 13 colorectal cancer patients out of 44 (30%) whose tumor DNA exhibited the methylation, using methylation‐specific PCR (MSP). To examine whether the cancer detection rate could be improved by using a different tumor marker, we examined the K‐ras status in 90 colorectal cancer patients using a mismatch ligation assay. Among the 31 patients showing K‐ras gene mutations in their tumors, the same mutations were observed in serum DNA of 11 patients (35%). Among the 90 patients, 63 showed tumors positive for K‐ras mutation or p16 promoter methylation, or both, and 22 had serum DNA positive for one or both. K‐ras mutation was found even in serum DNA of patients with Dukes A cancer, suggesting that colorectal cancer might be detected even in patients without symptoms by using this ligation assay.