INFREQUENT K-RAS ACTIVATION IN SUPERFICIAL-TYPE (FLAT) COLORECTAL ADENOMAS AND ADENOCARCINOMAS

Clinicopathological evidence is accumulating that a superficial-type ( nat) colorectal tumor is a distinct neoplastic entity. To clarify the genetic characteristics of this tumor, we investigated the K-ras gene mutations and morphological features of 43 tumors of this type. A muta tion of the K-ras codon 12 was detected in only 5 (16%) of 31 adenomas and 2 (17%) of 12 adenocarcinomas. The presence or absence of this mu tation was not correlated with the tumor size or stage or with histopa thological findings. None of these tumors had a mutation in codon 13 o r exon 2, including codon 61. This low incidence of K-ras mutations (1 6%) suggests that superficial-type colorectal tumors are etiologically distinct from ordinary colorectal polypoid tumors and that there may be an alternative pathway of colorectal tumorigenesis.