BACKGROUND: Flexible sigmoidoscopy is the standard screening test for colon cancer in asymptomatic individuals older than 50 years who do not have risk factors. It is assumed that a normal examination of the distal colon is associated with a reduced risk of proximal colon neoplasia. The authors of this study attempted to quantify the relative risk of advanced proximal colon neoplasia in patients with and without distal polyps.
POPULATION STUDIED: Employees of a pharmaceutical company and their family members who were 50 years or older were given the opportunity for free colonoscopic screening as a health benefit. The average age of the 1994 participants was 59.8 years, and 58.9% were men. Patients with a previous personal history of colorectal polyps, colorectal cancer, or inflammatory bowel disease and those with symptoms such as rectal bleeding, change in bowel habits, or recent abdominal pain were excluded.
STUDY DESIGN AND VALIDITY: This is a cross-sectional analysis of patients who received colonoscopy between 1995 and 1998. Patients were given information regarding the purpose of the study and were asked to call if interested in participating. A telephone interview was conducted to determine eligibility. Colonoscopy was performed by 36 gastroenterologists, and 97% of examinations reached the cecum. The size and location of polyps identified on colonoscopy were recorded before removal. Pathologists from the same center categorized and characterized the specimens. A limitation of the study is the absence of information about family history, particularly since patients with a positive family history may have been more likely to volunteer for participation.
OUTCOMES MEASURED: The main outcome of this study was the relative risk (RR) of advanced colonic neoplasia proximal to the splenic flexure in patients with and without distal colonic lesions. An advanced distal or proximal lesion was defined as a polyp or polypoid lesion with villous features, high-grade dysplasia, or cancer.
RESULTS: Of the 1994 patients studied, 61 (3.1%) had advanced distal neoplasia and 50 (2.5%) had advanced proximal lesions. This included 5 distal cancers and 7 proximal cancers. In patients with no distal lesions (78% of the population), 1.5% had an advanced proximal lesion. This was the reference group for the groups with pathological findings in the distal colon. The prevalence of advanced proximal lesions was 4.0% (RR=2.6; 95% confidence interval [CI], 1.1-5.9) in the group with distal hyperplastic polyps (10.1% of the population), 7.1% (RR=4.0; 95% CI, 1.9-8.3) in the group with distal tubular adenoma (8.4% of the population), and 11.5% (RR=6.7; 95% CI, 3.2-16.6) in the group with advanced distal neoplasms (3.1% of the population). Although the RR of advanced proximal neoplasia increased with the severity of distal lesions as expected, 46% of all advanced proximal neoplasms occurred in subjects with no distal lesions.
The risk of advanced proximal neoplasia is related to the severity of findings in the distal colon. Another study in the same issue1 also showed that a significant number of advanced proximal colon lesions go unrecognized with a standard flexible sigmoidoscopy investigation, even when combined with fecal occult blood testing. In fact, approximately half of the patients with advanced proximal colon neoplasia had no evidence of distal lesions. Although this study adds to a body of evidence that suggests that colonoscopy may have a role in screening for colon cancer, guidelines are needed that take into consideration not only these data but also cost, availability, and the impact of different screening modalities on mortality.