A team from Northern Ireland investigated the implications of this regional shift in the proximal distribution of colorectal cancer for the efficacy of flexible sigmoidoscopy as a screening tool.
The researchers obtained information on the site distribution of 5,153 colorectal carcinomas from the Northern Ireland Colorectal Cancer Register between 1990 and 1997. Data on an additional 1,241 colorectal cancer cases between 1976 and 1978 were made available from a previous study.
Data on the site reached by flexible sigmoidoscopy were obtained from a prospectively collected endoscopy database at one of Northern Ireland's main teaching hospitals for the period 1993-1998.
The team found that there was a significant proximal shift in colorectal cancer distribution between the two periods (23.5% proximal to the splenic flexure between 1976 and 1978 vs. 36.7% between 1990 and 1997).
|Flexible sigmoidoscopy may visualize fewer colorectal carcinomas if the proximal shift continues.
The descending colon was visualized during 74.4% of the sigmoidoscopy examinations.
By combining the observed extent of flexible sigmoidoscopy examination with colorectal cancer site distribution, it was calculated that the technique could have visualized 68.8% of colorectal carcinomas between 1976 and 1978. However, only 56.0% would have been observed between 1990 and 1997.
Extrapolating these data to a Northern Ireland screening program, involving flexible sigmoidoscopy and fecal occult blood testing, suggested that significantly more colorectal carcinomas could have been detected between 1976 and 1978 than between 1990 and 1997 (51.7% vs 48.2%, respectively).
Dr K McCallion, of the Royal Victoria Hospital, Belfast, concluded on behalf of the group, "This study confirms the previously documented left-to-right shift in colorectal cancer distribution in Northern Ireland.
"It demonstrates that if this shift continues, flexible sigmoidocopy will become less successful as a screening tool than is currently predicted."