Observations of aggressive, small, flat, and depressed colon cancer. Report of three cases.

Three cases of small, flat, and depressed colon cancers are reported. One lesion is less than 1 cm in diameter with lymphatic invasion in the submucosa; the other measures 0.8 cm in the longest dimension and penetrates through the muscular layers to the subserosa. The third one, 1.2 cm in diameter, has had liver metastasis. The endoscopic appearances of two lesions with a resected specimen are presented in color to demonstrate some difficulties in visualizing these lesions for endoscopists. The biologic aggressiveness of these three lesions appears due to their rapid growth, which is expressed by a high mitotic rate of the cancer cells. Their histogenesis is considered to derive from (1) flat adenoma, from (2) serrated adenoma, and (3) from hyperplastic epithelium (or de novo in origin), respectively.