Although colon cancer screening is recommended by many organizations, less clear is which method is best to detect tumors and precancerous lesions.
A new study in the New England Journal of Medicine suggests that a relatively inexpensive and non-invasive test may be just as effective as a colonoscopy.
Meanwhile, a 23-year study, also published in the journal, has confirmed that removing precancerous polyps, known as adenomas, during a colonoscopy can reduce the risk of death from colorectal cancer by half.
Based on the results, “an appealing concept would be to use colonoscopy as a triage screening test, offering it once for everybody at 60 years of age” and using it to classify people into high- and low-risk categories, Dr. Michael Bretthauer of Oslo University Hospital and Dr. Mette Kalager of Telemark Hospital, both in Norway, wrote in an editorial in the journal.
Low-risk people would not need further screening while those with adenomas would be evaluated regularly.
One in 20 Americans will develop colorectal cancer. About 140,000 cases are diagnosed in the United States each year, resulting in about 49,000 deaths, according to the National Cancer Institute. It is the third most common cancer worldwide.
The U.S. Preventive Services Task Force, a government-backed agency, recommends screening for people age 50 to 75 years by one of three methods: a colonoscopy every 10 years; annual stool testing; or a less-thorough look into the colon (known as flexible sigmoidoscopy) every five years in conjunction with stool testing every two to three years.
People often find the tests unpleasant. For example, in the new study that compared stool testing with colonoscopy, only 34 percent went along with stool testing. The participation rate was even lower when colonoscopy was offered, even though doctors can use it to cut away those suspicious precancerous adenomas.
Several tools may be used, either alone or together, to screen for colon cancer:
The first method is a stool test that checks your bowel movements for blood.
- Polyps in the colon and smaller cancers often cause small amounts of bleeding that cannot be seen with the naked eye.
- The most common method used is the fecal occult blood test (FOBT). Newer stool tests are called the fecal immunochemical test (FIT) and stool DNA test (sDNA).
The second method is a sigmoidoscopy exam.
- This test uses a flexible small scope to look at the lower part of your colon. Because it only looks at the last one-third of the large intestine (colon), it may miss some cancers.
- A stool test and sigmoidoscopy should be used together.
The third method is a colonoscopy. A colonoscopy is similar to a sigmoidoscopy, but the entire colon can be viewed. You will usually be mildly sedated during a colonoscopy.
Two other methods may be used:
- Double-contrast barium enemy, a special x-ray of the large intestine, which includes the colon and rectum
- Virtual colonoscopy - a type of x-ray that uses computer software to create an image
In theory, adenoma removal saves lives by preventing a tumor. Ann Zauber of the Memorial Sloan-Kettering Cancer Center in New York, chief author of the long-term evaluation of polyp removal, and her colleagues said their work demonstrates that.
“This study is showing both a reduction in colon cancer incidence and colon cancer deaths by removing the adenomas, and it’s a long-term effect” she said in a telephone interview. “This is reassuring for people to come in for screening.”
The conclusion is based on people who were sent for a colonoscopy between 1980 and 1990. The Zauber team compared their death rate to the estimated death rate from the Surveillance Epidemiology and End Results (SEER) program.
Over a period as long as 23 years, the rate from colorectal cancer among the 2,602 people who originally had adenomas removed was 53 percent lower than estimated from the SEER data. In all, 12 died from cancer in the removal group, while 25 had normally been expected to die of colorectal disease.
The lower rate includes the fact that 81 percent of the patients who had polyps removed continued to have periodic colonoscopies to check for growths.
Bretthauer and Kalager cautioned in their editorial that “the study mimics a situation in which 100 percent of the population complies with screening, which is not a real-life scenario.”