African-Americans have a high overall incidence of colorectal cancer and a greater prevalence of proximal or right-sided polyps and cancerous lesions. The right side of the colon includes the cecum, ascending colon and proximal transverse colon and cannot be reached by flexible sigmoidoscopy.
The reasons for higher incidence rates in African-Americans are unclear; however, dietary, nutritional factors, rates of physical inactivity, variability in screening rates, lower use of diagnostic testing, and increasing smoking rates have been most commonly implicated.
Dr. Roy D. Yen and his colleagues from the University at Buffalo and the VA Western New York analyzed the results of 587 colonoscopies (78 African-Americans, 502 Caucasians) performed at their institution in 2004. The number and location of polyps and presence of advanced lesions between the two cohorts were examined. They found significantly more African-American patients (14 percent) had advanced right-sided, or proximal, polyps compared to Caucasian patients (5.4 percent). Researchers also found more black patients had advanced polyps, proximal polyps and proximal colon cancers than whites.
Based on the results of this study, "Flexible sigmoidsocopy may be inadequate for colorectal cancer screening in this population. African Americans should undergo colonoscopy with particular attention for proximal lesions, however larger prospective studies are needed to confirm these findings," said Dr. Yen.
In a retrospective analysis conducted at The University Hospital and the New Jersey Medical School in Newark, NJ, Dr. Stanley H. Weiss, Dr. Mark J. Sterling, and their research team reviewed screening colonoscopies performed in 2005 and 2006. They found Latin Americans had a higher than expected incidence of polyps, pathologically significant lesions, and significant right-sided lesions, similar to previously reported findings in African-American patients.
Of the 756 screening colonoscopies, 287 (38 percent) were in Latin Americans and 331 (44 percent) were in African-Americans. Forty-eight percent of Latin Americans had pathologically significant lesions, compared to forty-six percent among African-Americans. The percentage of pathologically significant right-sided polyps was similar in Latin Americans (57 percent) and African-Americans (62 percent). However, researchers found that African-Americans were significantly more likely to have a large polyp (>1 cm) than Latin Americans and were more likely to have a large right-sided polyp.
According to study leader Dr. Stanley H. Weiss, "Because right-sided lesions are detectable with colonoscopy, which examines the whole colon, but not by flexible sigmoidoscopy, these findings have important implications for appropriate screening for colon cancer in Latin Americans."