Incidental carcinoma of the colorectum at autopsy and its effects on the incidence and future trends of colorectal cancers in Singapore.

Ten incidental invasive carcinomas (two early carcinomas involving the submucosa, and eight advanced carcinomas involving the muscularis propria or beyond) of the large intestine were discovered in a series of 1014 consecutive autopsies. All occurred in Chinese aged 60 years and older, constituting a prevalence rate of about 3% in this age group. If unsuspected colorectal carcinomas in Chinese Singapore residents aged 60 years and older exist in those who died in 1984 to the same extent as that noted in this autopsy study, it was estimated that 146 additional cases would have been added to the Cancer Registry in that year. This would constitute 47.9% of the total number of colorectal cancers diagnosed in this age group in 1984. This potential contribution has to be taken into consideration in epidemiologic studies on the incidence and future trends of colorectal cancers in Singapore. It was observed further that incidental carcinomas were found predominantly in the ascending colon. With more frequent use of colonoscopy, the incidence of right-sided cancers of the large bowel may be expected to increase. The current underdiagnosis of ascending colon carcinomas has to be taken into consideration when any future increase in right-sided cancers of the large bowel is observed.