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How is colon cancer diagnosed or evaluated?
Colon and rectal cancers are diagnosed using the screening tests mentioned below. These tests are used to detect precancerous polyps or cancer at a colon cancer stage early enough for removal and cure.
Digital Rectal Examination or DRE is used to detect tumors in the lower intestine, the rectum and the prostate. A lubricated-gloved finger is inserted into the patient's rectum by a doctor. The doctor feels for lumps or other abnormalities. Less than 10% of colon cancers can be evaluated this way.
Because blood in the stool or feces is not always visible to the naked eye, the fecal occult blood test (FOBT) is used to detect this hidden (occult) blood. The patient supplies up to six stool specimens in a specially prepared package. The stool is smeared on chemically treated paper, which will turn blue if blood is present.
When FOBT or DRE show signs of cancer, several techniques are available to help the physician visualize the colon. These include colonoscopy, sigmoidoscopy, and double-contrast barium enema.
Sigmoidoscopies are limited. This imaging technique only views the rectum and the left side of the colon. Colonoscopy and barium enemas allow the physician to view the entire large intestine.
Both flexible sigmoidoscopy and colonoscopy are invasive procedures that involve moving a fiber optic tube through the rectum and colon to view the intestinal walls. The tube contains a tiny camera that transmits the image to a video screen. The use of an ultrasound (sound wave) scanner can enhance viewing quality. During either sigmoidoscopy or colonoscopy, the physician is able to remove polyps or other abnormalities revealed by the procedures.
Colonoscopy is the most accurate testing method and can reduce cancer incidence by up to 90%. It is indicated for anyone with an increased risk for colorectal cancer, including those with a personal or family history of the disease. For about a day before the procedure the patient eats nothing and drinks a laxative solution that cleans out the colon. Air may be introduced into the intestine to widen it and allow the tube to navigate curves.
Other diagnostic tests include genetic screening, stool DNA testing and virtual colonoscopy.
Virtual Colonoscopy is an experimental technique that provides a three-dimensional image of the colon without using the invasive instruments used in the standard colonoscopy. The procedure itself involves pumping air into the colon and scanning the intestine using computed tomography (CT). It is very safe and takes only about 10 minutes. Follow up colonoscopy is needed if suspicious tissue is found.
There is also another exciting development in imaging of the digestive tract. Cancer research has yielded a small, pill-sized, video camera that can be swallowed. As it winds its way through the digestive tract, the camera beams data to a receiver worn by the patient. The camera is not a replacement for colonoscopy. More testing is needed to determine its value.
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