Adenomas, metaplastic polyps and other lesions of the large bowel: an autopsy survey.

Out of 1,014 large intestines examined, adenomatous polyps were encountered in 170 (16.8%) and metaplastic polyps in 67 (6.6%). Both types of polyps were more prevalent among the Chinese than the Malays and Indians. The prevalence rates corresponded to the relative risks for large bowel cancer for the respective ethnic groups. This suggests that causative factors such as dietary influence which are common to adenomatous polyps and cancer of the large bowel are operating at different levels among the different ethnic groups in Singapore. There are however, several factors between adenomatous polyp and colorectal cancer which are not congruent suggesting that the relationship between these two lesions though close is not a simple or direct one. On the other hand, the present study has shown several similarities between the epidemiological characteristics of metaplastic polyps and cancer of the large bowel. It is speculated that the causative factor(s) for metaplastic polyps may occur in association with carcinogen of the large bowel, but has an independent action. Consequently, while the metaplastic polyp may not itself be regarded as a premalignant lesion, the possibility that it may be a marker for increased risk for colon cancer is not excluded. Ulcerative colitis is rare in Singapore, and is not considered an important lesion in the pathogenesis of large bowel cancer in this country.