[Precancerous lesion in colorectal cancer]

Precancerous lesion in colorectal cancer was reviewed in terms of the evolution of the adenomacarcinoma sequence. K-ras codon 12 point mutation frequencies, examined in 157 adenomas, were observed in polypoid adenomas (67%) and flat adenomas (21%). Among flat adenomas, completely flat or depressed ones showed especially low mutation frequency (8%). K-ras mutation frequencies, examined in 70 invasive carcinomas, were observed in polypoid carcinomas (64%) and nonpolypoid ones (13%). From the results, it is suggested that polypoid adenomas develop into polypoid carcinomas and flat adenomas into non-polypoid carcinomas.