Colon cancer screening rates continue to lag behind those for breast and cervical cancer. In an editorial in the Feb. 20 edition of the Annals of Internal Medicine, Indiana University School of Medicine gastroenterologist and Regenstrief Institute, Inc. researcher Thomas Imperiale, M.D., writes that to increase screening rates for colorectal cancers, we need more convenient and less invasive screening tests. An infrequently used type of fecal sampling test, which has had Federal Drug Administration approval since 2001, may meet that need he says.
"In recent years, use of non-invasive screening has declined in favor of colonoscopy, but not everyone is willing to have a colonoscopy," said Dr. Imperiale, who is an IU School of Medicine professor of medicine. "The new immunochemical fecal occult blood test, referred to as I-FOBT, is a significant improvement over the older guaiac-based version. The newer fecal test has the potential to substantially increase screening rates for colorectal cancer, taking us back to the future in a sense." said Dr. Imperiale.
Unlike traditional fecal sampling tests which do not differentiate between blood from diet and blood from the digestive tract, I-FOBT uses antibodies to detect human blood in stool. This increased test specificity eliminates the need for dietary restrictions before colon cancer screening which may induce some individuals who are otherwise unwilling to take a screening test to do so.
Perhaps more importantly, the ability to choose different thresholds to indicate a positive result makes I-FOBT a test that can be used for individuals of any risk. "The test output (amount of hemoglobin per gram of stool) is a continuous variable, which means that a clinician can choose an I-FOBT positivity threshold to suit the patient's clinical characteristics such as age and reduce the chance of false positive test result," says Dr. Imperiale.
There are only a few examples of truly good screening tests for any cancer, according to Dr. Imperiale. He says that PAP smears are probably the best currently available screening tools because they are reasonably sensitive, specific and inexpensive, and the test itself has no risk. I-FOBT may be the comparable test for colon cancer screening, he concludes.
Colorectal cancer is the third most common cancer and the third leading cause of cancer related deaths in the United States. The National Cancer Institute estimates that more than 52,000 American will die of colorectal cancer in 2007.
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