In new colon cancer screening guidelines released earlier this year, an expert panel at the American Cancer Society for the first time expressly advocated tests, such as colonoscopy and sigmoidoscopy, over less invasive tests, such as fecal occult blood tests.
They did so because they argued that the more invasive procedures are aimed at detecting both polyps and cancer rather than malignancy alone.
The guidelines also included two new screening tests – stool DNA testing and CT colonography ("virtual colonoscopy").
"The science has made it clear that there are certain tests that have a higher potential to prevent cancer – and for the first time our guidelines state that colorectal cancer prevention should be the primary goal of screening," Dr. Durado Brooks, Director of Prostate and Colorectal Cancer at the ACS, said in a society news article in May.
The new guidelines, which were published in the May/June issue of CA: A Cancer Journal for Clinicians, show a preference for four screening modalities that the ACS believes can spot both colorectal polyps (a potential precursor to cancer) and cancer. Those modalities are:
- Flexible sigmoidoscopy performed every 5 years.
- Colonoscopy performed every 10 years. These first two tests involve a flexible tube tipped with a small camera; polyps can be removed upon discovery. With colonoscopy, doctors view the entire length of the colon, while sigmoidoscopy views only the lower one-third.
- Double contrast barium enema every 5 years. With this test, a barium-laden liquid is admitted into the colon via catheter. X-rays are then used to spot abnormalities.
- CT colonography (virtual colonscopy) every 5 years. In this test, the colon is first widened with air, then CT scanning helps pick up polyps or cancer.
There are also 3 types of non-invasive stool tests that are aimed primarily at detecting malignancy, not polyps. They are:
- Guaiac-based fecal-occult blood testing (gFOBT) once a year.
- Fecal immunochemical test (FIT) annually. Both of the first two screens look for blood in stool.
- Stool DNA test. This test is relatively new, and looks for cancer-linked DNA in stool.
More research is needed to determine how frequently it needs to be done, the ACS says. A positive result on any of these stool-based screens necessitates further follow-up with colonoscopy, the guidelines say.
The new guidelines were devised by ACS experts with help from the US Multi Society Task Force on Colorectal Cancer and the American College of Radiology, and apply to men and women age 50 and over with an average risk of developing colorectal cancer. Individuals at higher risk (due to family history, for example) may need earlier or more frequent screening.
Colorectal cancer rates have started to decline in recent years, but the malignancy remains the third most common cancer diagnosis in the United States and the second biggest cancer killer overall, the ACS notes.
Early detection is crucial: According to the ACS, 90% of patients with localized colorectal cancer will survive 5 years after diagnosis but if the cancer has spread to other parts of the body 5-year survival falls to just 10%.
Those statistics can be turned around if more Americans engage in regular screening, however.
"The best test is the test the patients can get and will take," Brooks said. "But patients should be aware that there is a greater potential for certain types of tests to prevent cancer."
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