The discrepancy of histologic diagnosis between flat early colon cancers and flat adenomas

Although flat or depressed early colon cancer (FDEC) has increasingly been reported, its incidence is highly variable among medical institutions in Japan. We recently encountered 7 patients with a flat or depressed colonic lesion, which was completely resected by operative local excision or floatation excision biopsy (strip biopsy) including surrounding mucosa. Apparent discrepancy was noted in the histologic diagnosis between two experienced pathologists. One pathologist, associated with an institution where there has been no report of FDEC, diagnosed only one lesion as carcinoma in an adenoma with submucosal invasion and all the other lesions as flat adenomas. The other pathologist, associated with an institution where there has been a number of reports of FDEC, diagnosed 5 of 7 lesions as FDEC. These results suggest that different criteria used in each institution may be a major cause of the difference in the detection rate of FDEC.