Introduction
"Similar to the recommendations on screening for prostate cancer (see AAFP Related Articles) and on tight monitoring for glycemic control in diabetes presented by Dr. [Steven] Woolf, the recommendations for colorectral cancer are not plainly clear," offered Ted Ganiats, MD, in his discussion on colorectal cancer (CRC) screening, second in a series of clinical recommendations updates delivered at this year's AAFP Scientific Assembly.
CRC remains an important health problem, and unlike other illnesses such as lung cancer, compelling evidence does exist that screening for CRC can reduce mortality. Over 134,000 new CRC cases and 55,000 CRC deaths occured in 1996 alone.
Which Test to Use
Given the possible screening tests, including fecal occult blood tests (FOBT), flexible sigmoidoscopy, double-contrast barium enema, and colonoscopy, two questions face many physicians: which test should we be using, and to whom should we administer it?
FOBT, Ganiats asserted, is the only test whose benefit has been proved by randomized trials. When used yearly, a 30% reduction in cancer deaths can be realized. When used every other year, the test achieves a lower -- but still substantial impact on decreasing mortality. Unfortunately, using yearly FOBTs results in false positives in up to 40% of the population over a 10-year period, necessitating colonoscopy for follow-up. Given the high false-positive rate leading to colonoscopy, it is possible that direct visualization primarily would show better results. Flexible sigmoidocsopy has some case-control evidence which reveals a beneficial effect even after 10 years of follow-up, while neither barium enemas nor colonoscopy has direct experimental evidence of benefit for screening.
What Do Patients Want?
With only the evidence in the literature, FOBT would seem to be the clear winner. However, patient preference plays a role in choosing a screening method. While FOBT is the cheapest, the high false-positive rate and resultant high colonscopy rate need to be considered. Going right to colonoscopy, on the other hand, has a higher rate of complications, is much more expensive, and demands clinical resources if applied on a wholesale basis that doesn't currently exist.
In addition, patients need to be aware that the large relative reductions in cancer deaths don't translate to high absolute-risk reductions. In the published trial of FOBT screening, a 33% reduction in cancer deaths over the 10 years of follow-up in the trial was reported, and only 80 (rather than 120) cancer deaths occured in the 15,000 patients screened. Ganiats also discussed the results of a study he performed to assess patient preferences for different screening tests . While there was no dominant preference for one screening method over another, among patients who had already undergone a colonoscopy, over 70% would have the test again, dwarfing other "preference for repeat" rates, presumably because of patient's understanding of the need to follow up other positive screening tests with colonsocopy. The Big Question
Given that 1) colorectal cancer screening is a good practice, 2) patient preferences affect compliance, and 3) patient education affects patient preferences, the big question becomes how the busy family physician can educate patients about the colorectal cancer screening options. Clearly physicians do not have the time to spend carrying out these important elements of screening. One potential solution is to have non-physician office staff heavily involved with patient education.
Guidelines for Colorectal Cancer Screening?
There will continue to be variation in tests chosen by different practitioners. As solace for the fact that no definitive evidence exists on the best screening method for CRC, Ganiats offers the AAFP's current recommendations (see Recommended Links), which provide for FOBT as well as sigmoidoscopy every 5 years for low-risk patients over 50 years of age.
Physicians who want to use FOBT can feel comfortable with a standard FOBT screen (three slides with two samples per slide), either recommending a restrictive diet 3 days before or not, depending on how acceptable false positives are to you and your patients. The most important recommendation is to choose some form of screening for CRC, rather than letting patients go without screening.
References
Winawer, et al: Colorectal Cancer Screening: Clinical Guidelines and Rationale. Gastroenterology: 112(2):594-692, 1996.
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