Histogenesis of small colonic adenocarcinomas.

It has been claimed that in order to identify the type of mucosal lesion which precedes colonic adenocarcinoma only those tumours measuring < or = 1 mm in diameter should be considered. The review of the English literature indicates that only 35 colorectal adenocarcinomas measuring < or = 1 cm in diameter have been so far reported. From the three cases of colonic adenocarcinoma measuring 8 mm or less in diameter presented here, one adenocarcinoma originated in a flat adenoma, the second in an exophytic tubular adenoma, and the third showed no adenomatous component. It would thus appear that colonic adenocarcinomas can originate not only from exophytic adenomas or from flat adenomas but also from apparently nonadenomatous flat mucosa.