Diagnosing Colorectal Cancer

Most, if not all, colon cancers develop from polyps. Screening is extremely important for detecting polyps before they become cancerous. It can also help find colorectal cancer in its early stages when you have a good chance for recovery.

Like many people, you may be embarrassed by the screening procedures, worried about discomfort or afraid of the results. Try not to let these concerns stand in your way. Most procedures are only moderately uncomfortable, and working with a doctor you like and trust should help ease your embarrassment. If you question the results of your screening, ask for a second opinion. Keep in mind, however, that risks are associated with the more invasive screening procedures.

Common screening and diagnostic procedures include the following:

• Digital rectal exam. In this office exam, your doctor uses a gloved finger to check the first few inches of your rectum for large polyps and cancers. Although safe and painless, the exam is limited to your lower rectum and can't detect problems with your upper rectum and colon. In addition, it's difficult for your doctor to feel small polyps.
• Fecal occult (hidden) blood test. This test checks a sample of your stool for blood. It can be performed in your doctor's office, but you're usually given a kit that explains how to take the sample at home. You then return the sample to a lab or your doctor's office to be checked. The problem is that not all cancers bleed, and those that do often bleed intermittently. Furthermore, most polyps don't bleed. This can result in a negative test result, even though you may have cancer. On the other hand, if blood shows up in your stool, it may be the result of hemorrhoids or an intestinal condition other than cancer. For these reasons, many doctors recommend other screening methods instead of, or in addition to, fecal occult blood tests.
• Flexible sigmoidoscopy. In this test, your doctor uses a flexible, slender and lighted tube to examine your rectum and sigmoid — approximately the last 2 feet of your colon. Nearly half of all colon cancers occur in this area. The test usually takes just a few minutes. It can sometimes be somewhat uncomfortable, and there's a slight risk of perforating the colon wall.
• Barium enema. This diagnostic test allows your doctor to evaluate your entire large intestine with an X-ray. Barium, a contrast dye, is placed into your bowel in an enema form. During a double contrast barium enema, air is also added. The barium fills and coats the lining of the bowel, creating a clear silhouette of your rectum, colon and sometimes a small portion of your small intestine. This test typically takes about 20 minutes and can be somewhat uncomfortable. There's also a slight risk of perforating the colon wall. A flexible sigmoidoscopy is often done in addition to the barium enema to aid in detecting small polyps that a barium enema X-ray may miss, especially in the lower bowel and rectum.
• Colonoscopy. This procedure is the most sensitive test for colorectal cancer and polyps. Colonoscopy is similar to flexible sigmoidoscopy, but the instrument used — a colonoscope, which is a long, flexible and slender tube attached to a video camera and monitor — allows your doctor to view your entire colon and rectum. If any polyps are found during the exam, your doctor may remove them immediately or take tissue samples (biopsies) for analysis. This is done through the colonoscope and is painless. If you have adenomatous polyps, especially those larger than 5 millimeters in diameter, you'll need careful screening in the future.
A colonoscopy takes about a half-hour. You may receive a mild sedative to make you more comfortable. Preparation for the procedure involves drinking a large amount of fluid containing a laxative to clean out your colon — enemas are no longer necessary. Major risks of diagnostic colonoscopy include hemorrhage and perforation of the colon wall. But these risks are rare. Complications may be somewhat more frequent when polyps are removed.
• Genetic testing. If you have a family history of colorectal cancer, you may be a candidate for genetic testing. This blood test may help determine if you're at increased risk of colon or rectal cancer, but it's not without drawbacks. The results can be ambiguous, and the presence of a defective gene doesn't necessarily mean you'll develop cancer. Knowing you have a genetic predisposition can alert you to the need for regular screening. Still, you'll also want to consider the psychological impact of what the test may reveal. Knowing you may develop cancer affects not only your own life, but the lives of everyone close to you. Genetic testing for children is even more complex and problematic. It's best if you discuss all of the ramifications of genetic testing with your doctor or a medical geneticist.
• New technologies. In the future, new technologies, such as virtual colonoscopy, may make colon screening safer, more comfortable and less invasive. In virtual colonoscopy, you have a two-minute computerized tomography scan, a highly sensitive X-ray of your colon. Then, using computer imaging, your doctor rotates this X-ray in order to view every part of your colon without actually going inside. Before the scan, your intestine is cleared of any stool, but researchers are looking into whether the scan can be done successfully without the usual bowel preparation. Although virtual colonoscopy potentially is a tremendous step forward, it's not as accurate as regular colonoscopy and doesn't allow your doctor to remove polyps or take tissue samples. This test is also not widely available.
Another new test checks a stool sample for DNA from abnormal cells. In preliminary studies, the test has proved to be so accurate it may eventually eliminate the need for more-invasive examinations such as colonoscopy, at least in average-risk circumstances. A three-year clinical trial of this test by the National Cancer Institute is under way.