Dis Colon Rectum  1997 Feb;40(2):161-7 

Ki-ras point mutation in different types of colorectal carcinomas in early
stages.

Kojima M, Konishi F, Tsukamoto T, Yamashita K, Kanazawa K.

Department of Surgery, Jichi Medical School, Tochigi, Japan.

PURPOSE: The aim of this study was to elucidate pathways of carcinogenesis in
the colon and rectum by investigating Ki-ras point mutation in different types
of colorectal carcinomas in the early stage. METHODS: We analyzed rates of
Ki-ras codon 12 mutations in 34 small, polypoid-type carcinomas (Tis or T1), 21
superficial-type carcinomas (Tis or T1), and 42 advanced carcinomas (T2, T3, and
T4). RESULTS: Frequency of Ki-ras mutations in superficial-type carcinomas was
14.3 percent (3/21), which was significantly lower than 50 percent (17/34) in
small polypoid carcinomas and 40.5 percent (17/42) in advanced carcinomas. These
data suggest that another pathway of colorectal carcinogenesis that does not
involve Ki-ras point mutation might exist. Among the 17 small polypoid
carcinomas with Ki-ras point mutation in which both adenomatous and
carcinomatous tissue were examined, 12 showed a mutation of the same type in
both carcinomatous and adenomatous tissues. In two cases, mutation was present
only in carcinomatous tissue and not in adenomatous tissue; in the other three
cases, Ki-ras point mutation was present only in adenomatous tissue but not in
carcinomatous tissue. CONCLUSIONS: These data suggest that carcinoma in a small
polypoid lesion does not always develop from pre-existing adenoma with Ki-ras
point mutation; in a small number of the polypoid-type early carcinomas,
polyclonal composition concerning the Ki-ras gene may exist.

PMID: 9075750 [PubMed - indexed for MEDLINE]