Ask An Oncologist

Your doctor has been nagging you to get that screening colonoscopy, and you've been putting it off for years. The last thing you want to do have someone look up your rear with a long tube! 

Finally you have an alternative--a non-invasive colon cancer-screening test! No day spent in the bathroom with laxatives, no hospital procedures, and no expensive insurance co-payments. You've heard about it on TV or social media:  Cologuard™. What is it? Should you do it?  Can it replace colonoscopy?  

Why should you get screened for colon cancer?

Colon cancer--or more accurately, colorectal cancer, which includes both the colon and rectum--is one of the most common cancers, but it is relatively infrequent, as only about 4.5% of people will develop it over their lifetime. It is the cause of 50,000 deaths in the US per year. Unlike many other cancers, colon cancer has a good chance of cure if it is detected early, when it is completely silent and there are no symptoms. The purpose of a screening test is to detect these early stage cancers. If everyone in the country were screened for colon cancer, about half of these deaths could have been prevented--maybe yours, too.

Colorectal cancer screening is recommended to start at age 50 for those who have an average risk of colon cancer. Your doctor can determine if your risk is average and a screening test is appropriate. All colon cancer-screening tests need to be ordered by a physician, who will have the ability to interpret the results and provide follow-up.

Who should not get a colon cancer-screening test?

People whose cancer risk is above average may need to be evaluated more thoroughly than with a simple screening test, and may need to start at a younger age. These include those who have had a previous history of bowel cancer, colon polyps, or inflammatory bowel disease, or who have a strong family history of colon cancer--they will need more detailed evaluation than a simple screening test, and may have to start at a younger age. Cancer screening tests should also not be done if there are any persistent symptoms--such as bleeding from the bowels, pain, or weight loss. The symptoms might be due to something other than cancer, but they will need evaluation to determine the cause and the treatment.  A screening test doesn't give the cause of symptoms; it can only say whether or not a cancer is present. A negative test may give a false sense of security.

How often should you get colon cancer screening?

The current recommendations are that anyone with an average risk of colon cancer should get screened with colonoscopy at age 50, and then every 10 years if the screen is negative. Medicare and most insurance policies will pay for a screening colonoscopy every 10 years, which is the estimated time it takes for a new cancer to grow from a completely normal bowel. If a growth such as a polyp is found during the procedure, then the colonoscopy will have to be repeated sooner than ten years, possibly 1 to 3 years, depending on what is found. Of course, if a cancer is found, then evaluation and treatment will begin.  

What does colonoscopy involve and why are people so reluctant to do it?

Many people object to the idea of having a long, flexible tube passed into their rectum, with doctors crowded around to have a look. In reality this is never experienced, because the patient is under anesthesia during the procedure; he will just go to sleep and wake up without any memories of what went on.

The true objection to colonoscopy is that the bowel has to be completely cleaned out before the procedure. This means eating nothing but clear liquids for a full day before the procedure, taking several rounds of laxatives and purgatives, and spending much of the day in the bathroom. 

What is the Cologuard™ test?  

Cologuard is a proprietary method in which a sample of a person's stool is analyzed to extract DNA, and the DNA is tested for mutations in the genes involved in cancer. To perform this test, the subject has to collect a small sample of a bowel movement, place it in a special collection container, and send it to the Cologuard lab. The lab will perform the tests and send the report to the doctor who ordered the test. You might want to visit the test's web site, cologuardtest.com.

Can Cologuard be done instead of a colonoscopy?

Cologuard is 92% sensitive--that means it will miss only 8% of cancers. So a negative test is likely to be correct most of the time. Cologuard is 87% specific, which means that about 13% of the time there will be a positive test when there is no cancer present. If you have a positive test, then you will have to have a full colonoscopy, but there is a still some chance that you don't have cancer.

Most experts feel that Cologuard is a good alternative for a screening test in people of average risk, and it beats not doing anything at all. Still, there isn't much long-term experience with it yet. Some experts feel that the Cologuard test should be performed every three years instead of ten. That's probably because unlike colonoscopy, Cologuard doesn't detect polyps, which take about three years to develop into cancer. The American Cancer Society recommends colonoscopy every 10 years as preferred, but a DNA-based stool test as an alternative every 3 years.  The US Preventive Services Task force says screening should start at age 50, and recommends that patients decide with their doctors which test is best for them; the frequency will depend on the test.

What are you waiting for?

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