Abstract: AIM: To detect sequence and mutation of K-ras oncogene in tissue and stool DNA of patients with colorectal cancer in order to provide a method of noninvasive and simple colorectal cancer diagnosis.METHODS: DNA was separated and purified from colorectal cancer tissue or stool of patient with colorectal cancer, then the K-ras gene was amplified by PCR and PCR products were cloned, the K-ras gene was sequenced, and the mutation was identified.The expression of color colorectal cancer antigen was inspected by immunohistochemical technique.Stool sample of patient with colorectal cancer was detected with enzyme-linked immunosorbent assay (ELISA).RESULTS: K-ras gene sequence of the stool was completely same as that of the tissue of the patient; K-ras mutation was detected in one case.There was relativity between the mutation of K-ras gene and the pathology type of colorectal cancer and the expression level of colorectal cancer antigen in stool sample.CONCLUSION: It is feasible that colorectal tumors can be detected by a noninvasive method based on the molecular pathogenesis of the disease.Detecting K-ras gene mutations of stool DNA can provide bases for the screening, early detection, and prognosis to patients with colorectal cancer.

Key words: colorectal cancer, K-ras gene, gene mutation, colorectal cancer monoclone antibody, DNA from stool