Led by gastroenterologist Thomas F. Imperiale, M.D., professor of medicine, researchers are assessing risk factors to determine who needs more invasive screening with colonoscopy and who may be screened sufficiently with less invasive methods. The results of their initial risk factor study are published in the December 16 issue of the Annals of Internal Medicine.
The researchers viewed the colonoscopy results of nearly 2,000 people over the age of 50 and developed a risk index for colorectal cancer, identifying factors associated with an increased probably of finding the disease in the upper colon, an area that only can be viewed with a colonoscope. The researchers then tested how well the risk index worked using data from an additional 1,031 people 50 and older.
They found three factors increased the chances of finding advanced, pre-malignant growths in the upper colon: older age, being male and having certain types and sizes of polyps in the lower colon, which can be seen by less invasive and less costly sigmoidoscopy.
"The risk index we have developed may identify low-risk people whose probability of advanced precancerous growths in the upper colon is about one in 250," says Dr. Imperiale, who also is a research scientist at the Regenstrief Institute Inc. "This index is a first step toward identifying people who do not require colonoscopy after sigmoidoscopy; however, colonoscopy could be considered later in their life, as their risk changes."
The shorter flexible tube of the sigmoidoscope can be used to examine the lower half of the colon. If this exam finds polyps, the colonoscope is used to view the upper half of the colon. The colonoscopy is more invasive, more costly, and poses small but serious risks to some patients.
"The risk-to-benefit ratio of colonoscopy is not favorable for everyone," Dr. Imperiale noting that those in the lowest risk category of the study were women in their 50s who had a no polyps on sigmoidoscopy. Dr. Imperiale currently is involved in a study to consider additional risk factors including family history of colorectal cancer.
Cancer of the colon or rectum is the second leading cause of cancer deaths in the United States. Polyps – outgrowths on the wall of the colon – precede most colorectal cancers. Screening procedures can detect polyps before they become cancerous and can be removed during colonoscopy or surgically.
The study was funded by the National Institutes of Health. For more information about the Regenstrief Institute Inc. at the IU School of Medicine, go to www.regenstrief.org.
Journal
Annals of Internal Medicine