New screening guidelines

New colorectal cancer screening and surveillance guidelines published by the US Multisociety Task Force on Colorectal Cancer stress the importance of initial screening for people age 50 and older and reduce the frequency of surveillance for the majority of patients who have had colon polyps removed.

Studies suggest that initial colorectal cancer (CRC) screening provides the best results. A patient’s first screening detects the largest, most dangerous polyps, which can be removed during a colonoscopy in a procedure called polypectomy. Previous guidelines recommended that after polypectomy, patients should be given follow-up colonoscopies every three years. However, data show that follow-up colonoscopies every three years. However, data show that follow-up colonoscopies after three years may not add significant benefit to many patients, because polyps with important pathology are very unlikely to develop in that brief time period.

The new guidelines recommend patients who have one or two small (less than 1 cm.) tubular adenomas have their first follow-up colonoscopy at five years. Patients with advanced or multiple adenomas (greater than or equal to three) should still have their first follow-up colonoscopy at three years, as recommended previously. Planning follow-up surveillance of patients according to their risk for advanced adenomas is an especially important point in the new guidelines, stresses, lead author of the guidelines, from Memorial Sloan-Kettering Cancer Center in New York. If adopted nationally, this would shift critical resources from surveillance to screening, helping us screen more people, which would in turn decrease incidence and mortality rates. In addition to recommending risk stratification for post-polypectomy patients, the new guidelines differ from the earlier version in a number of ways:

Colonoscopy is recommended instead of barium enema for diagnostic evaluation, for screening people with close relatives who have colorectal cancer or adenomatous polyps before age 60, for screening people with two affected close relatives, for screening people with possible genetic mutations that predispose them to colorectal cancer and for surveillance after polypectomy and after CRC resection. Colonoscopy allows us to visualize the entire colon and to detect and remove polyps in one procedure. It’s invaluable in patients who are at high risk of developing colorectal cancer. Patients with Familial Adenomatous Polyposis (FAP), a syndrome caused by genetic mutation, run a risk of CRC approaching 100 percent. Genetic testing should be considered in patients with FAP who have relatives at risk. If family members test negative, they are considered at average risk for colorectal cancer.

If family members test positive, they should follow up with sigmoidoscopies until they develop polyps, at which point the timing of a colectomy is considered. Genetic testing in children can be delayed until age 10. Genetic counseling should guide genetic testing and considerations of colectomy (removal of the colon) for those with family members carrying genetic mutations. Hereditary nonpolyposis colorectal cancer (HNPCC), a genetic mutation, account for up to two percent of colon cancer cases. People with HNPCC should have a colonoscopy every one or two years beginning at age 20 to 25, or 10 years earlier than the youngest age of colon cancer diagnosis in the family, whichever comes first. Genetic testing for HNPCC should be offered to first-degree relatives of persons with a known inherited gene mutation. The new guidelines analyze two approaches to genetic testing to find HNPCC among high-risk families.

Previous guidelines recommends double-contrast barium enema (DCBE) screening every 10 years, but because it is less sensitive than colonoscopy, the interval has been shortened to five years. DCBE is included as an option in the guidelines because it is widely available. However, it detects only about half of colon polyps, including large polyps. Yearly fecal occult blood test (FOBT) is recommended for people age 50 or older who are at average risk for colorectal cancer. Rehydration is not recommended: although rehydration of the guaiac-based slides increases sensitivity, the readability of the test is unpredictable and substantially increases the false positive rate. Guideline authors looked to the future of colorectal cancer screening and two new tests that are in development. Virtual colonoscopy (thin-section, helical, computed tomography followed by off-line processing), can yield high-resolution, three-dimensional images of the colon.

A new DNA stool test is under study. Research shows these test sensitivities to be more than the FOBT, but less than colonoscopy. Trials evaluating the performance of the test are still in progress. Colorectal cancer screening should take place with the tests available now, and not wait until something better comes along. The colorectal cancer screening tests we have today are very effective to screening tests for other cancers that are more widely used.