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Flat neoplasms in the adenoma-carcinoma sequence in Japan.

Flat adenomas have a higher risk of association with adenocarcinoma than the protruded type, and flat cancer has a tendency to invade deeply despite its small size. Furthermore, it has been suggested that flat, small carcinomas readily invade through the muscularis mucosa into the submucosa and are associated with an increased risk of early metastasis into lymph nodes, as compared with polypoid growth pattern cancers. It has become evident that these lesions are becoming more common in Japan, as well as in some western countries. It has been generally believed that the colon is comparable to the stomach in terms of endoscopic diagnostic capability and accuracy. Therefore, we were surprised to learn that flat neoplasms, including flat or depressed adenomas and cancers, exist in the colon, as they seem to have previously been overlooked. Recent significant advances in endoscopic resolution and the development of improved diagnostic techniques and modalities may play an important role in the detection of such lesions. In the present study, the diagnosis and management of such lesions, along with their genetic background, is reviewed. Some techniques for their detection currently being used in Japan will also be reviewed using several actual cases.