Screening for colon cancer

August 8, 2011

Screening for colon cancer can be done in many ways. The choice of which screening is best for the patient should be based on his/her preferences and the available resources for testing and follow-up. The physician or health care provider should explain the benefits and potential risks associated with each option before deciding on the screening process.

The frequency of screening is based upon the test. If the FOBT cards are used, three cards must be collected every year. There may be false-positive results where the test can indicate the presence of blood when there is nothing wrong with the colon. The U.S. Preventive Services Task Force is a body of experts that evaluates the effectiveness of screening tests based on the clinical evidence, the magnitude of benefit, and potential risks. The task force strongly recommends that clinicians screen men and women at the age of 50 years and older for colorectal cancer.

The method of screening is still under debate. There are different options and different benefits of each option. There is good evidence that periodic FOBT reduces mortality from colorectal cancer and fair evidence that sigmoidoscopy alone or in combination reduces mortality. The standard in practice is three stool cards collected yearly and sigmoidoscopy performed every 5 years, beginning at the age of 50. Recent studies have suggested that colonoscopy, which is a full examination of the entire colon, can find more cancers because there is direct visualization of the entire colon. Colonoscopy is the most sensitive and specific test for finding cancer in polyps (meaning that most of the cases it detects are really cancer and most of the ones it says are not cancer are really not cancer), but does come with higher risk than the other screening tests. The risks are small, but include a risk of bleeding and perforation, usually related to removal of polyps or biopsies. The colonoscopies require an overnight bowel cleansing preparation, mild sedation, highly trained personnel to do the test, and a longer recovery time. At this point, the task force feels that it is not certain whether the potential added benefits of colonoscopy, relative to the other screening alternatives, are large enough to justify the added risks, cost, and inconvenience for all patients. This is an area that will continue to be evaluated. A colonoscopy for screening purposes need only be done every 10 years.

The age at which colorectal cancer screening should be stopped is not known. In general, screening has been done in patients younger than 80 years of age. In theory, the yield should be higher in older persons, that is, we should find more cancers in older persons. However, the benefits may be limited as a result of the other medical conditions of the patient that may affect the treatment of any cancer that could be found. It is appropriate and reasonable to stop screening in patients whose age or comorbid conditions limit their life span.

The FOBT requires three consecutive stool samples be obtained at home and brought into the clinic. It has not been established whether the patient should avoid certain foods or medications. However, adding water to the specimens before testing them, does increase the sensitivity of finding blood. It is important to remember that three different stool cards from spontaneously voided stools are the standard and that neither a rectal examination nor the testing of a single specimen obtained during a rectal examination is considered adequate screening. A combination of both FOBT and sigmoidoscopy may detect more cancers. It is highly recommended that the stool cards, that is, FOBT cards, be returned before the sigmoidoscopy. A positive test on an FOBT is an indication for a colonoscopy. The sigmoidoscopy should not be performed in the presence of a positive stool card.

SEE ALSO: Cancer, Pain, Preventive care


Category: Colorectal Cancer