Small nonpolypoid carcinomas of the large intestine.

Two small carcinomas of the colon were examined, one an intramucosal carcinoma and the other a small carcinoma invading the submucosa. Serial sections did not reveal any adenomatous hyperplasia or polyps in the vicinity. The colonoscopist must be aware of the potential clinical importance of any small mucosal excrescence. Although several studies have indicated that most colonic carcinomas develop from an adenomatous polyp, some carcinomas apparently arise de novo. Further study of the epidemiologic, etiologic, and prognostic factors relating to these apparently uncommon lesions is indicated.