title: Lower incidence of K-ras codon 12 mutation in flat colorectal adenomas than in polypoid adenomas.
abstract: In order to clarify genetic changes in flat adenomas, K-ras codon 12 point mutations were examined in 56 flat adenomas, 81 polypoid adenomas and 42 cancers of colon and rectum. The mutation frequency in flat adenomas was 23% (13/56), significantly lower than that in polypoid adenomas (67%: 54/81) and cancers (76%: 32/42). Even mildly dysplastic adenomas or small (less than 5 mm) adenomas showed higher mutation incidence in polypoid type (62%, 57%) than in flat type (23%, 19%). Among flat adenomas, flat elevated lesions exhibited relatively higher mutation frequency than completely flat or depressed ones. As for cancers, 14 tumors (33%) contained mutations only in a minor tumor cell population, indicating that these mutations occur at a late stage of tumorigenesis. These results suggest that the adenoma-carcinoma sequence through flat adenomas may be different from that through polypoid adenomas, and genetic changes may be heterogeneous in colorectal carcinogenesis.
authors.affiliation: First Department of Surgery, University of Tokyo.
authors.forename: S
authors.initials: S
authors.lastname: Yamagata
authors.forename: T
authors.initials: T
authors.lastname: Muto
authors.forename: Y
authors.initials: Y
authors.lastname: Uchida
authors.forename: T
authors.initials: T
authors.lastname: Masaki
authors.forename: T
authors.initials: T
authors.lastname: Sawada
authors.forename: N
authors.initials: N
authors.lastname: Tsuno
authors.forename: T
authors.initials: T
authors.lastname: Hirooka
mesh_terms: D000236:Adenoma / Q000235:genetics* / Q000473:pathology; D018256:Adenomatous Polyps / Q000235:genetics* / Q000473:pathology; D001483:Base Sequence; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D004252:DNA Mutational Analysis; D017931:DNA Primers; D004273:DNA, Neoplasm / Q000235:genetics; D005787:Gene Frequency; D011905:Genes, ras; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity
chemical_list: D017931:DNA Primers; D004273:DNA, Neoplasm