Screening for colon cancer has been proven to save lives, by detecting and removing polyps and early-stage cancers before they can cause serious trouble. Unfortunately, many people don't get screened when and how they should, putting themselves at unnecessary risk for a devastating disease. There is a lot to understand about colon cancer screening. For starters, let's review what tests are available and how they are used.
All colon cancers start out as polyps, but not all polyps turn into cancer. There are two main types of polyps. Adenomas are growths of slightly abnormal cells within the colon. Over time, they can become cancerous, which is why they should be removed whenever possible.
Hyperplastic polyps are just simple folds of the colon lining, and are not actually true polyps at all. They can look very similar to adenomas when seen on a CT scan or viewed through a colonoscope. However, when examined under a microscope, they are clearly different from adenomas, and hyperplastic polyps never develop into cancer.
The simplest, but least precise method of looking for colon cancer is to check for blood in the stool. Polyps and cancers often leak small amounts of blood, but only intermittently and usually not enough to change the appearance of the stool. These tiny amounts of blood can be detected with a stool occult blood test.
"Occult" (hidden) refers to the fact that this test can detect minimal amounts of blood that aren't visible to the naked eye. All you need to do is smear a tiny amount of stool on a special test card and bring or send it back to the lab. Since cancers and polyps don't bleed all the time, samples from 3 separate bowel movements should be checked in order to maximize the reliability of this test.
The stool occult blood test is very non-specific. Certain foods (especially red meat) can cause a false-positive result. Also, any source of blood from the mouth all the way down to the rectum can cause a true-positive occult blood test. Most of the time, blood in the stool is due to gastritis, hemorrhoids, or other non-cancerous problems. But a positive test always deserves careful thought and evaluation, both to rule out cancer and to determine if there are any other medical issues that need treatment.
The other way of screening for colon cancer is to look directly at the inner walls of the colon. Many decades ago, this was done with a rigid tube inserted into the rectum, called a sigmoidoscope. Needless to say, this was an uncomfortable procedure at best. It was also limited by the fact that only a small portion of the colon could be inspected. This was eventually replaced by flexible sigmoidoscopy, which caused less discomfort and allowed a little more of the colon to be seen.
Most experts agree that sigmoidoscopy should no longer be a part of routine colon cancer screening, because it doesn't allow the entire colon to be examined. There are, however, still some situations in which sigmoidoscopy is appropriate as part of a colon cancer screening program, so check with your physician if that is what he or she is recommending for you.
The primary method of looking at the colon today is by colonoscopy, in which a long flexible tube with a fiberoptic light on its tip is slowly advanced into and all the way through the colon. Polyps and any other suspicious lesions can be removed or biopsied, and other treatments can be performed when necessary. Colonoscopy is performed under sedation ("twilight sleep"), which blocks out pain and memory, but allows the patient to remain awake and cooperative.
An alternative to colonoscopy is a specialized CT scan called colonography or virtual colonoscopy, which doesn't require sedation or insertion of a long tube into the rectum. While this may sound attractive, I believe that colonoscopy is a better test than CT colonography in most cases, and I'll explain why in greater detail in a future entry.
The biggest discomfort associated with both of these methods of looking at the colon is the need to completely clean out the bowel in advance, so that any polyps and growths can be clearly seen by the physician. Typically, the clean-out involves some combination of laxatives and/or enemas, and often results in several hours on the toilet passing lots of watery stool.
In summary, we have two methods to screen for colon cancer: checking for blood in the stool and looking directly at the inside of the colon. All of these tests are unpleasant to some degree, and I believe that is why many people don't get screened as frequently as they should (or even at all). But consider this question: Is it better to periodically undergo an unpleasant test, or to risk the pain, indignity, and premature death associated with colon cancer and its treatment?
