Clinical significance of depressed-type colorectal neoplasms based on growth and development

A route of colorectal cancer development other than the adenoma-carcinoma sequence has recently become an issue due to the discovery of depressed-type early colorectal cancers. Moreover, the fact that some polyp-like cancers actually originate from depressed-type lesions has become obvious. Despite the protruding shapes of depressed-type early colorectal cancers, they probably have biological characteristics, which are different from those of the usual polyp lesions. We undertook this study to evaluate the clinical significance of depressed-type colorectal neoplasms. The authors recently experienced 87 cases of depressed-type colorectal neoplasms. Using Kudo's classification, we classified these 87 cases into three types based on their growth patterns, type IIc, type IIa + IIc, and type Is + IIc, and then analyzed these types on the basis of size, type, and submucosal invasion rate. The submucosal invasion rate of cancers of type IIa + IIc was significantly higher than that of type IIc (p < 0.05), and the rate for cancers of types IIa + IIc and Is + IIc together was significantly higher than that of type IIc (p < 0.05). However, no significant difference was found between the rates of types IIa + IIc and Is + IIc. In conclusion, the IIa + IIc and Is + IIc sub-types of depressed-type colorectal neoplasms, individually and together, have higher rates of submucosal invasion than type IIc lesions. Accordingly, type IIa + IIc and type Is + IIc must be differentiated from the usual polyps and should be managed cautiously, despite their protruding shapes.