Colonic carcinoma resembling submucosal tumor: report of a case and review of the literature.

Submucosal tumor-like colorectal carcinoma, most of whose surface is covered with normal mucosa, is very rare. We report a case of colonic carcinoma resembling submucosal tumor. A 54-yr-old man visited our institution for an evaluation of a positive fecal occult blood test. Colonoscopic examination revealed a small, mainly red polypoid lesion with a central deep ulceration and many white spots in the sigmoid colon. Indigocarmine staining demonstrated that the white spots were faint shallow depressions. Magnifying colonoscopic examination showed that the lesion surface, except for the ulceration and the depressions, was covered with normal mucosa. Although the tumor was small, we strongly suspected its malignancy due to a deep ulceration. As we could not excise it endoscopically, we performed sigmoidectomy. The lesion was 12 mm in size. Histologic examination revealed that the lesion was a moderately differentiated adenocarcinoma that was mainly covered with normal mucosa, that carcinoma was exposed only at the ulceration and the depressions on the surface, and that it had expanded to the muscularis propria. Together with considerations from the literature, this type of colorectal carcinoma is supposed to be invasive and surgical resection should be considered, no matter how small it may be.