Early Colorectal Cancer with Special Reference to the Superficial Nonpolypoid Type from a Histopathologic Point of View

The incidence and histopathologic characteristics of nonpolypoid (superficial type) early colorectal carcinomas were studied and compared with those of the polypoid type. The superficial type was subclassified as elevated (type IIa), type IIa with central depression (type IIa+IIc), plain (type IIb), depressed (type IIc), and IIc with marginal elevation (type IIc+IIa). The superficial type comprised 22% and 27% of intramucosal and submucosal carcinomas, respectively. Pure type IIb was not found, and there were only three pure type IIc lesions. Type IIa+IIc and IIc+IIa (and IIc) showed a significantly higher rate of submucosal invasion among the small tumors (59% and 71% less than 20 mm, respectively) compared to the polypoid type; type IIa showed no significant difference. The incidence of lymph node metastasis among submucosal carcinomas showed no significant difference between the superficial type and the polypoid type. About 64% and 52% of type IIa and IIa+IIc tumors accompanied residual adenoma, suggesting that they originated from small, flat adenomas through the adenoma—carcinoma sequence, whereas type IIc+IIa (and IIc) did not have an adenomatous component, implying that they arose de novo or originated through an adenoma—carcinoma sequence at a smaller size than the type IIa and IIa+IIc lesions. Superficial‐type early colorectal carcinomas are not rare, and they are not uniform in nature. Rapid growth and invasion to the submucosa is characteristic of superficial‐type lesions with a central depression, and only superficial depressed (type IIc+IIa, IIc) lesions can arise de novo. Although they grow rapidly to invade the submucosa, it cannot be said that they show more aggressive behavior than the polypoid type.