New blood test for colon cancer screening: Questions remain

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In April, the U.S. Food and Drug Administration (FDA) approved a new screening test for colorectal cancer, commonly referred to as colon cancer. This test is unique because it’s blood-based – meaning no more stool samples or the dreaded colonoscopy. Patients can have the test done as part of their annual blood tests, and they don’t have to think twice about it.

But what it lacks in discomfort it makes up for in inexactitude. This newly approved test is not as sensitive or as accurate as a colonoscopy or as a Fecal Immunochemical Test (FIT), which can detect hidden blood in stool, potentially indicating colon cancer. Rates of colon cancer have declined significantly since the 1980s with an even bigger drop in recent years, according to the American Cancer Society. From 2008-2010 the rates of colon cancer fell by 4% each year. This decline can be attributed both to changes in lifestyle habits and to an increase in colon cancer screenings.

Colon cancer is still the second leading cause of cancer death in the United States among men and women, but it has potential to move down the rungs of the mortality ladder. Over a third of those eligible for screening are currently not getting tested. There are people who have never been tested, and that population needs to be reached if we want the decline of colon cancer to continue.

Few symptoms appear in early stages of colon cancer, which is one reason these screening tests are so important. Dr. Andrew Chan, associate professor of medicine at Harvard Medical School and a practicing gastroenterologist at Massachusetts General Hospital, says an important aspect of a screening test its ability to affect outcomes. As in, does the test detect cancer early enough for a physician to successfully treat it? Studies of this new blood test have shown otherwise.

Dr. Chan says, “Options that are much more established and much more effective should be offered first.”

One advantage of this test is its ability to screen the 35% of people who are not being screened at all. “For most of us in the field of cancer prevention, we feel that any screening test is better than no screening test at all,” Chan said. But he worries this convenient test will lull patients into a false sense of security. Testing negative for colon cancer with this test does not necessarily prove the patient doesn’t have any precancerous growths, called polyps, or other signs of early colon cancer. This test detects late-stage cancers more successfully than it does early stages, but by then it might be too late to get treatment. Dr. Chan also says that colon cancer prevention should also include lifestyle changes like increased physical activity, decreased smoking, and a better diet of fruits and vegetables.

“I think this new test is worth a conversation with your doctor.” Dr. Chan says. “Just remember the devil is in the details, and there are limitations with this test.”

The U.S. Preventative Services Task Force — an independent panel of experts in primary care and prevention — recommends colon cancer screening for adults between the ages of 50 and 75. Those screening tests include high-sensitivity fecal occult blood testing (FOBT), sigmoidoscopy, or colonoscopy. Your doctor can advise you on the best screening tests and schedule for you based on your family history and risk factors.

• FOBT –One type uses a chemical to detect blood in the stool, and the other, referred to as a Fecal Immunochemical Test (FIT), uses antibodies. These tests screen stool samples for analysis and should be done annually as either a part of an at-home test or at the doctor’s office.
• Flexible sigmoidoscopy – For this test, the physician inserts a lighted tube into the lower third of the colon to look for polyps and other signs of cancer. This test is recommended every 5 years with the FOBT and every 3 years without it.
• Colonoscopy – This test is very similar to the flexible sigmoidoscopy, but the physician inspects the entire colon rather than only a part of it. Precancerous polyps can be removed during the procedure, and this test is recommended every 10 years.