PURPOSE:Recently it became obvious that some early cancers which appeared to be polyp lesions had actually originated from depressed-type lesions. The aim of this study was to clarify both the characteristics of depressed- type early colorectal cancers compared with protruded- or flat-type ones and the significance of a subclassification of depressed-type early cancers. METHODS:The authors experienced 248 early colorectal cancers from 1996 to 2000. We classified those cancers into protruded, flat, and depressed types based on growth and development. Further, we used Kudo's classification to subclassify the depressed-type cancers into three sub-types, IIc, IIa+IIc, and Is+IIc. We analyzed the 248 cases with emphasis on size, type, sub-type, and submucosal cancer (sm) rate. RESULTS:The sm rate of the depressed cancers was 81.8% (18/22) and was significantly higher than those of the protruded (30.5%) or the flat (38.5%) types (P<0.05). The sm rate of the depressed lesions not larger than 10 mm was 70% (7/10) and that of the lesions from 11 mm to 20 mm was 91.7% (11/12); there were no depressed cancers larger than 20 mm in diameter. The sm rate of the type IIa+IIc plus type Is+IIc lesions was higher than that of type IIc lesions (93.3%, 14/15 vs. 57.1%, 4/7). Endoscopic resection was done in 74.2% of all early colorectal cancers. CONCLUSIONS:The sm rate of depressed-type early colorectal cancers was 82%, and no depressed cancers were larger than 20 mm in diameter, suggesting that by the time a depressed-type cancers had become larger than 20 mm in size, it had already progressed into an advanced cancer. Thus, it is very important to detect depressed-type cancers in an early stage. Moreover, it is imperative to differentiate type IIa+IIc and type Is+IIc from polyp lesions and to manage them cautiously because their sm rate is higher than that for type IIc lesions.