According to a University of Pittsburgh-led study published in the December issue of Gastroenterology, medium-sized polyps found in the colon with flexible sigmoidoscopy and subsequently evaluated by full colonoscopy are associated with a significant number of advanced adenomas (high-risk polyps) and cancers.
These findings raise questions about taking a "wait and watch" approach to medium-sized polyps and delaying referral to colonoscopy, a strategy which could become more popular with newer screening tests that are observational and do not remove polyps, such as virtual colonoscopy.
The study included 10,850 men and women enrolled in the Prostate, Lung, Colorectal and Ovarian Cancer (PLCO) Screening Trial, a randomized, community-based study evaluating the effectiveness of cancer screening tests on site-specific mortality at 10 centers throughout the United States. The participants in the study had an abnormal flexible sigmoidoscopy with at least one detectable polyp and subsequently underwent a diagnostic colonoscopy within one year.
"An emerging issue in colorectal cancer screening is the management of medium-sized polyps, since many new technologies under development can only observe the lining of the colon, and do not offer the ability to remove polyps," said Robert Schoen, M.D., M.P.H, lead author of the study and professor of medicine and epidemiology, University of Pittsburgh School of Medicine. "With these new methods, colonoscopy and polyp removal are required as second procedures, but because of issues of expense and risk, determining a specific threshold for subsequent procedures becomes an important issue. One area of uncertainty concerns medium-sized polyps. In our study, individuals with medium-sized polyps 0.6 - 0.9 cm were found to have a significant yield of advanced adenomas and even cancer, making an observational strategy in this setting potentially risky."
In the study, polyps 0.6 - 0.9 cm were found in 2,183 men and 1,426 women through flexible sigmoidoscopy, in which a scope is used to examine the inside of the large intestine from the rectum through the descending colon. Flexible sigmoidoscopy differs from colonoscopy in that only a portion of the colon is examined, whereas with colonoscopy the entire colon is examined. When the men and women in the study underwent diagnostic colonoscopy within a year, 14.5 percent of the women and 15.9 percent of the men were diagnosed with advanced adenomas (pre-cancerous polyps or growths in the lining of the large intestine that are at higher risk for developing into cancer), and 0.6 percent of the women and 0.7 percent of the men were diagnosed with cancer. In some cases, the medium-sized polyps were considered large when removed and assessed at colonoscopy. In other cases, the small polyps had important, adverse pathologic characteristics once removed and studied under the microscope.
"The implication of our study is that where we draw the line when assessing and evaluating polyp size and referral to colonoscopy has to be carefully considered," said Dr. Schoen. "These results offer a cautionary note to waiting and watching."
Colorectal cancer is a worldwide public health problem. In the United States, colorectal cancer accounts for 11 percent of all cancers, with 148,610 new cases and 55,170 deaths expected by the end of 2006. For patients with advanced disease, five-year survival rates are 10 percent to 20 percent. When colorectal cancer is diagnosed at an early, localized stage, the five-year survival rate is 90 percent.
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