OBJECTIVETo explore the value of detection of adenomatous polyposis coli (APC) gene and K-ras gene mutations in fecal and blood samples in colorectal neoplasm screening.

METHODSFrom 84 subjects undergoing colonoscopic examination (including 31 with colorectal carcinoma, 26 with colorectal adenoma, and 27 healthy subjects) between October, 2003 and March, 2004, 5 ml of heparinized peripheral blood and 3-5 g fecal specimens were collected. The DNA was extracted from the specimens for detecting the mutation of APC and K-ras gene using polymerase chain reaction-single strand conformation polymorphism and the results were analyzed statistically.

RESULTS AND CONCLUSION(1) The incidence of APC gene mutation was 41.9% and 57.7% in the plasma, and 34.8% and 26.8% in the fecal specimens of colorectal carcinoma patients and adenoma patients, respectively, both higher than that in normal subjects (P<0.05), suggesting high consistency between fecal and plasma APC gene mutation detection (K=0.811, P<0.05). (2) The incidence of plasma K-ras mutation was 48.4% in colorectal carcinoma patients, 3.8% in adenoma patients and 0% in normal control subjects, and in the feces, the incidences were 54.8%, 7.7% and 11.1%, respectively. The mutation rate was higher in carcinoma patients than in adenoma patients and normal subjects (P<0.05). Fecal K-ras gene mutation detection was consistent with plasma detection (K=0.662, P=0.000). (3) APC gene mutation detection showed a low sensitivity and specificity in the diagnosis of colorectal carcinoma, but K-ras mutation detection showed a high specificity. The diagnostic sensitivity increased when combining APC and K-ras gene detection in the plasma or fecal specimens, but there was no evidence to suggest that APC and K-ras mutation detection in the plasma could be better than detection in the feces. (4) For colorectal carcinoma, APC gene mutation is associated with lymphoid node metastasis, but not with the patient's gender, age, tumor location, differentiation, distant organ metastasis or CEA level (P>0.05), and the mutation of K-ras gene is related to the degree of tumor differentiation.