August 13, 2014
News Review From Harvard Medical School -- New Home Test Finds Most Colon Cancers
U.S. regulators have approved a new home test that detects more than 90% of colorectal cancers. The Food and Drug Administration (FDA) approved the Cologuard test August 11. Like the older fecal occult test, Cologuard checks for microscopic amounts of blood in stool. But the new test also looks for abnormal DNA. This helps to find cancers that don't bleed. The test is done at home. The person collects a stool sample and mails it to a laboratory for analysis. In a study, nearly 10,000 men and women were given 3 types of tests: a fecal occult test, the Cologuard test and a colonoscopy. Colonoscopy is considered the most accurate test for colorectal cancer. It uses an instrument to look inside the colon. Cologuard detected 92% of the cancers that colonoscopy found. The fecal occult test detected 74%. Cologuard also found 69% of the polyps that were considered most likely to turn into cancer. The fecal occult test found 46%. Cologuard is made by Exact Sciences Corp. It is intended for screening of people ages 50 to 85 who have no symptoms of colorectal disease and an average risk of colon cancer. HealthDay News wrote about the FDA decision.
By Howard LeWine, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
In March, a panel of advisers to the U.S. Food and Drug Administration (FDA) weighed the risks and benefits of a more sensitive home stool test to screen for colorectal cancer. All of the panel members voted to recommend approval. As expected, the full FDA now has followed the panel's advice.
The test goes by the trade name Cologuard. It is approved for people age 50 and over who are at average risk of colon cancer. It should not be used as a substitute for colonoscopy in people with greater than an average risk. This includes people with:
- A history of polyps or prior colorectal cancer
- A strong family history of colorectal cancer
- Ulcerative colitis or Crohn's disease
Until now, approved stool testing for cancer screening only checked for microscopic amounts of blood. This method misses a lot of polyps and small cancers.
Cologuard detects abnormal DNA as well as blood. A very large study concluded that with the DNA detection the test misses only 8% of people with colorectal cancer. This compares with 26% missed by testing only for blood in the stool.
Both tests missed many pre-cancers. But Cologuard missed fewer of them than the stool tests that detect blood only.
However, the Cologuard test produced more false positives than just testing stool for blood. A false positive stool test suggests that you have a polyp or cancer when none actually exists. The only way to prove that a stool test is a false positive is to perform a colonoscopy to directly look at the whole colon. That's why anyone with a positive stool test done for cancer screening needs a colonoscopy.
What Changes Can I Make Now?
Cologuard stool testing offers another option for colorectal cancer screening. But right now, colonoscopy remains the best screening method. It is recommended once every 10 years for people age 50 and over who have an average risk of colorectal cancer.
The doctor uses a flexible, lighted instrument called a colonoscope. You receive medicine to help you relax and avoid discomfort. The doctor looks through the colonoscope and inspects the inside of the colon.
The great advantage of colonoscopy is that it does more than detect early cancers and pre-cancers. It finds polyps. If the doctor finds a polyp, a device on the end of the colonoscope can remove it. Removing polyps helps prevent them from turning into cancers.
Colonoscopy does have risks. It's possible that the instrument can puncture the colon and cause an infection. It's also possible to have excessive bleeding if the doctor removes a polyp or snips a bit of tissue for a biopsy. Fortunately, these risks are small.
Other options available to screen for colorectal cancer are:
- Sigmoidoscopy every five years -- This test is similar to colonoscopy, but it looks at only the lower part of the colon. No sedation is needed. The preparation is much simpler than it is for a colonoscopy.
- Virtual colonoscopy -- This test uses a CT scan instead of a scope to check the colon for cancers and polyps. It is not covered by Medicare.
As with stool testing, if something abnormal is found on one of these tests you would need a full colonoscopy.
What Can I Expect Looking to the Future?
While the FDA was reviewing the expert panel's advice, the U.S. Centers for Medicare & Medicaid Services was doing the same. It is very likely that Medicare will approve the Cologuard test to screen people ages 50 to 85 at average risk for colorectal cancer. Future studies will determine how often the test should be done if no cancer is detected. Some experts suggest the interval might be once every 3 years.