Mutations in the Ki-ras gene detected in colorectal biopsy specimens

M Beranek PhD^a, J Bures Prof MD PhD^b, S Rejchrt MD PhD^b, K Dedic MD PhD^c, Prof Palicka MD PhD^a

^aInstitute of Clinical Biochemistry and Diagnostics, Charles University Hospital, Hradec Kralove, Czech Republic, ^bClinical Centre of Internal Medicine, ^cDepartment of Pathology; Charles University Hospital, Hradec Kralove, Czech Republic

AIM: Development of colorectal adenocarcinoma is known to be associated with the presence of a lot of molecular genetic changes in colon cells. Somatic mutations in the Ki-ras gene (12p12.1) belong to the crucial events occurring approximately in the middle of the colon neoplastic cascade. Many studies dealt previously with DNA analyses in resected tumors. In this work we tried to detect the presence of Ki-ras mutations in specimens of colorectal polyps and tumors obtained bioptically, and consequently to identify these mutations. METHODS: 50 bioptic specimens of hyperplastic polyps, adenomatous polyps, and colorectal carcinomas from 28 men and 22 women with a median age of 69 years (range 19 – 86 years) were examined. As controls we used 11 bioptic samples of morphologically normal colonic mucosa from 6 men and 5 women with a median age of 57 years (range 42 – 71 years). Mutant-enriched PCR-RFLP analyses at Ki-ras codons 12 and 13 were used. Identification of the mutations was carried out by nucleotide sequencing of PCR products. RESULTS: Ki-ras mutations were found in 8 of 18 (44%) carcinomas and in 8 of 19 (42%) adenomatous polyps. Mutations were detected neither in the hyperplastic polyps nor normal colonic tissue. Sequencing analysis revealed that a GGT to GTT transversion is the most common genetic change appearing in Ki-ras gene codon 12. It was identified in 50% of the carcinomas and 71% of the adenomas with Ki-ras mutations. In codon 13, a GGC to GAC transition was detected in one adenoma. CONCLUSIONS: Our data demonstrate that the bioptic specimen of colonic tissue is suitable biological material for detection of point mutations in the Ki-ras gene. The incidences of the mutations in carcinomas and big adenomatous polyps in the colon seem to be very similar. Taking into account aggressivness of some Ki-ras mutations, a proper DNA analysis could contribute to improvement of laboratory diagnostics of cancer, especially in the subjects at a higher risk for colorectal carcinoma.

Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in poster session 893 (Molecular pathology).