Proportion of Flat- and Depressed-Type and Laterally Spreading Tumor Among Advanced Colorectal Neoplasia

BACKGROUND & AIMS: Flat-and depressed-type neoplasias along with laterally spreading tumors (LSTs) have been reported in colorectal neoplasias. We estimated the prevalence of flat and depressed types and LSTs along with their proportion among advanced neoplasias in a large average-risk population undergoing screening colonoscopy. METHODS: This was a cross-sectional study performed at a single, general community institution, with subjects who were 40 to 79 years old, asymptomatic, and who had undergone their first colonoscopy for screening between 2003 and 2009 (n = 4910). Among the neoplasias detected, advanced neoplasias were morphologically classified as the polypoid type, flat and depressed type, or LST. We determined the prevalence and proportion for each type among the advanced neoplasias, with morphologies defined according to the Japanese endoscopic classification. RESULTS: Advanced neoplasias were detected in 7.9% of men, 4.7% of women, and 6.1% of overall subjects. The polypoid type, the flat and depressed types, and the LSTs accounted for 75.3%, 7.5%, and 17.2% of advanced neoplasia, respectively. There was a high proportion of T1 cancers among the depressed types (40%). Approximately 80% of LSTs were located on the right side of the colon and more than 30% of LSTs showed high-grade dysplasia or T1 cancer. CONCLUSIONS: Most advanced neoplasias detected were of the polypoid type. LSTs accounted for a considerable proportion among advanced neoplasia and tended to be located on the right side of the colon. The influences of any LSTs need to be taken into consideration for preventing colorectal cancer.