Screening for colon cancer using a flexible tube - which is less invasive and more convenient than colonoscopy - may also help prevent new cases and deaths from the disease, a new study suggests.
In a large trial of more than 150,000 older U.S. adults, those who were randomly assigned to get screened using so-called flexible sigmoidoscopy on two different occasions were 21 percent less likely to get colon cancer than those not offered the screening.
They were also 26 percent less likely to die of cancer, probably because screening picked up pre-cancerous lesions and early-stage cancers before they could cause serious harm, researchers reported Monday in the New England Journal of Medicine.
Colonoscopy “is a very unpleasant thing,” said Dr. Alfred Neugut, an epidemiologist and oncologist from Columbia University in New York, who wasn’t part of the study team.
“Sigmoidoscopy is a much less elaborate procedure, so you can basically walk into the doctor’s office and get it on the spot… and it’s much less invasive,” he said.
Screening Saves Lives
Colorectal cancer almost always develops from precancerous polyps (abnormal growths) in the colon or rectum. Screening tests can find precancerous polyps, so that they can be removed before they turn into cancer. Screening tests can also find colorectal cancer early, when treatment works best.
When Should I Begin to Get Screened?
You should begin screening for colorectal cancer soon after turning 50, then continue getting screened at regular intervals. However, you may need to be tested earlier than 50 or more often than other people if—
- You or a close relative have had colorectal polyps or colorectal cancer.
- You have inflammatory bowel disease.
- You have genetic syndromes such as familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer.
Speak with your doctor about when you should begin screening and how often you should be tested.
Flexible sigmoidoscopy is one of three colon cancer screening methods recommended by the U.S. Preventive Services Task Force, a government-backed body that sets screening guidelines.
Flexible sigmoidoscopy utilizes a flexible sigmoidoscope, a flexible, fiberoptic viewing tube with a light at the tip. It is inserted through the anus and is used by the doctor to examine the rectum and the part of the colon adjacent to the rectum. It is a shorter version of a colonoscope. Approximately 50% of colorectal cancers and polyps are found to be within the reach of a flexible sigmoidoscope. It is recommended that individuals of average risk for colon cancer undergo a flexible sigmoidoscopy examination at age 50 and every 3-5 years thereafter. If polyps are found during a flexible sigmoidoscopic examination, a colonoscopy to examine the entire colon is recommended to remove the polyps as well as to find and remove additional polyps in other parts of the colon. The removed polyps are examined by a pathologist under a microscope to determine if the polyps are benign, malignant or pre-cancerous. Individuals with precancerous polyps (adenomas and villous adenomas) have a higher than average risk of developing colon cancer, and it is recommended that they return periodically for surveillance colonoscopies.
The Task Force says that annual fecal occult blood testing, flexible sigmoidoscopy every five years with fecal testing every three years or colonoscopy every 10 years are all options for adults aged 50 to 75 at average risk of cancer.
But many Americans in that age group still don’t get screened - and one of the reasons may be the discomfort of preparing to get a colonoscopy, including taking laxatives, and the inconvenience and invasiveness of the procedure itself.
What is the best colon cancer screening test?
Colonoscopy is the only method that has a high sensitivity for all polyps - small and large - and that can remove them during the procedure. CT colonography or virtual colonoscopy can miss small or flat lesions but has the advantage of being less invasive. It still requires a complete bowel cleansing prior to the procedure. If an abnormality is seen during virtual colonoscopy, a colonoscopic examination will still be needed to verify the finding or for polyp removal. Other, newer screening procedures include testing for abnormal DNA in the stool or the combination of a flexible sigmoidoscopy and a barium enema. The barium enema is suggested if colonoscopy is not available. However, for the removal of polyps, there is only one procedure that is currently useful, and that is colonoscopy.
Are colorectal screening tests done by your general practitioner or should they be done by gastroenterologists or other experts?
There are several types of colorectal cancer screening tests. Fecal occult blood tests (FOBT) are usually provided by your general practitioner for you to take home and then return to the laboratory for development and analysis. Flexible sigmoidoscopy, which evaluates the lower third of the colon with an endoscope, is performed by some but not all general practitioners. Colonoscopy is a more extensive endoscopic evaluation of the entire length of the colon and is generally done by gastroenterologists or other gastrointestinal specialists. Colonoscopy is considered the gold standard for colorectal cancer screening by the American Cancer Society and many more professional organizations. It is highly recommended that your primary care provider refer you to a board-certified gastroenterologist or endoscopist to have the test done.
The new findings provide more evidence that sigmoidoscopy as an initial test - followed by colonoscopy only in the case of positive findings - may be a valid alternative, researchers said.
The data come from the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, which compared new cases of cancer and cancer-related deaths in adults who did or didn’t get different types of screening.