Abstract
Sixty-one nodule-aggregating tumors and 131 non nodule-aggregating flat elevations were compared clinicopathologically. Characteristics of nodule-aggregating tumors was demonstrated as follows; 1) Tumors were predominantly found in the rectum and cecum. 2) The size of adenoma, m-cancer and sm-cancer was about twice as that of non nodule-aggregating flat elevations, although the depth of invasion was less despite of the larger size. 3) In many cases cancers were accompanied by adenoma components. Histologically, adenoma or adenoma components associated with cancer was usually characterized by tubulo-villous type. This tendency was more remarkable in larger tumors. 4) Compared to non nodule-aggregating flat elevations, the incidence of whitish tumors was higher and reddish ones lower. In particular, this tendency was more remarkable for adenoma. 5) Larger tumors contained vertically higher parts, in which cancer and sm invasion were confirmed histologically. These findings indicate that nodule-aggregating tumors essen-tially characterized by horizontal growth manifest vertical growth in accordance with malignant transformation or development of sm invasion. The lower frequency of adenoma than m cancer, among nodule-aggregating lesions, suggests the possibility of overlooking the diagnosis of adenoma. When nodule-aggregating lesions were defined as those over 20 mm in diameter, the difference in the frequency of adenoma and m-cancer became more evident. No difference in localization was noted between tumors over 20 mm in diameter and smaller ones. When lesions less than 20 mm in diameter were included, the size went in an ascending order from adenoma to m-cancer to sm-cancer. From these findings it seems appropriate to include nodule-aggregating flat elevations in nodule-aggregating lesions irrespective of their size.
