Colonoscopy is widely known as a powerful screening/early detection test for colorectal cancer, capable of preventing, or so it was thought, up to 90% of cancers. However, recent studies show that colonoscopy misses many cancers, according to the New York Times in an article by Gina Kolata.
A newly published Canadian study documents the low success rate of colonoscopy in picking up cancer in the right side of the colon, an area where 40 percent of cancers occur. In the left side of the colon, the area directly above the rectum, where cancers should be easier to detect, colonoscopy missed a third of occurrences.
Does that mean patients should dismiss colonoscopy as an ineffective test? Quite the contrary. Although colonoscopy is now found to prevent only 60% of colon cancer deaths, it’s still “a good test,” said Dr. Ransohoff, gastroenterologist at the University of North Carolina. In the Times article, Kolata points out that colonoscopy works relatively well, in contrast with other screening tests: Mammograms prevent 25 percent of breast cancer deaths and the Prostate-Specific Antigen (PSA) test has not been proven to prevent prostate cancer deaths.
In addition, patients can help maximize colonoscopy’s effectiveness by doing their homework. Dr. Douglas Rex, Indiana University’s director of endoscopy and professor of medicine, said that polyps in the colons may be obscured if patients did not thoroughly cleanse the bowels. Taking half of the laxative the night before the test and the other half in the morning – a procedure not always done – can help clear out patients’ systems and improve the visibility of the inner wall of the colon.
Researchers also urge patients to seek out the best colonoscopists who are skilled in performing the test consistently. Patients should ask how many colonoscopies the doctor does each year (a good volume would be three to four colonoscopies a day), what percent of those turn up polyps (it should be around 25% in men and 15% in women; much lower suggests that the doctor is missing some), and how long the scope is in the colon (colonoscopists should take at least eight minutes to withdraw the endoscope; too short a time suggests a hurried look).