4492 Depressed type early colorectal cancer.

Background: Depressed colorectal lesions are believed, at least in Japan, to play an important role in colorectal carcinogenesis. Ten years ago they were considered extremely rare, but recently more and more similar cases have been found not only in the Orient but also in the West. Aims: To clarify the characteristics of depressed colorectal lesions, comparing them with those of protruded or flat polyps. Methods: During the period from April 1996 to Sep 1999, 4072 colorectal adenomas and cancers were detected by total colonoscopy in our institute. The patients presented with symptoms and/or signs such as bloody stool, fecal occult blood, or polyps detected by barium enema study. Some of them underwent the colonoscopy as a regular check-up after polypectomy or colectomy. The colonoscopic examinations were done using magnifying scopes (Olympus 200Z), with frequent spraying of indigo carmine dye. Results: The lesions were divided into three groups; protruded polyps (2006), flat adenomas (1973), and small depressed lesions (93). The number of colorectal cancer was 476; Dukes A 226, Dukes B 151, Dukes C 99. The rates of invasive cancer among protruded polyps were 0.2% in lesions from 5 to 9 mm in diameter, 1.7% in 10- 14mm, 4.0% in 15-19mm, and 7.3% in 20-29mm. The respective rates among the depressed lesions were 33%, 64%, 75%, and 100%. Thirteen of the depressed lesions were accompanied by large polyps (including six colon cancers) which were considered to be causing the symptoms or signs leading to the colonoscopic examination. In order to detect and diagnose small depressed lesions, chromoscopy and magnifying colonoscopy were indispensable. Conclusion: Depressed lesions of colorectum are more malignant than protruded or flat polyps. They do not present any specific symptoms or signs but tend to be associated with large polyps or cancers. They are detected only by the eyes of the examiners who are familiar with such lesions.