Definition and Overview
Also known as colorectal cancer or bowel cancer screening, colon cancer screening is any of the examinations that are meant to diagnose the presence of colon cancer or polyps that may lead to cancer in the rectum and the colon.
In the United States, more than 130,000 men and women are diagnosed with the disease every year while at least 50,000 die from it, making it one of the most common causes of death for both men and women.
The screening exams are helpful in catching cancer while it is still in its early stages, increasing the chances of survival and delaying the progression of the disease in the process.
The screening includes different tests, with various levels of benefits and risks. Sometimes, one test is enough. However, it is common for doctors to request a combination of the tests to provide a more accurate diagnosis.
These tests include:
Colonoscopy – a test that involves passing a flexible tube called a colonoscope into the colon. It can be used to detect the presence of polyps, as well as remove them.
Sigmoidoscopy – a test that involves passing a flexible tube called sigmoidoscope that reaches the rectum and the colon’s lower section.
Virtual colonoscopy – an imaging test that views the colon using CT scan.
Double-contrast barium enema – an imaging test that can help detect abnormalities of the colon using an X-ray.
Fecal occult blood test – a lab test that confirms if there’s blood present in the stool. This is based on the belief that the blood vessels of the tumour or the polyps are prone to rupture, which then leads to bleeding. This test is more comprehensive than the standard stool examination since it can detect blood that cannot be seen by the naked eye.
Who Should Undergo and Expected Results
The screening test is recommended for men and women who are between 50 and 75 years old. Those who are already 76 years old and above may no longer be advised to take the exam as the risks may be greater than the benefits. Meanwhile, sigmoidoscopy, virtual colonoscopy and double-contrast barium enema should be taken every five years and colonoscopy every 10 years. Fecal occult blood test should be carried out every year.
There are, however, exceptions to the rule especially if patients are considered high risk. These are individuals who have:
- Family history of the cancer or polyps
- Inflammatory disease affecting the bowel, such as Crohn’s disease and ulcerative colitis
- Lynch syndrome (also called hereditary non-polyposis colorectal cancer caused by inherited genes)
- Familial adenomatous polyposis (inherited disorder characterized by the recurrent appearance of adenomatous polyps in the lining of the large intestine)
- Abnormal consumption of tobacco and alcohol
Patients who fall into any of these categories are encouraged to take the screening tests early, before 50 years old, and in a more frequent interval.
The results depend on the type of colon cancer screening test performed. Exams such as colonoscopy and flexible sigmoidoscopy may be carried out to find both cancer and polyps. The fecal occult blood test, on the other hand, can detect cancer but not polyps. Further, since sigmoidoscopy only reaches the lower half of the colon, it may not find cancer and polyp in the upper region. Virtual colonoscopy is comprehensive and can detect even small polyps that may not be seen through a regular colonoscopy.
The level of discomfort can also be varied. Some of the tests require preparation while exams such as virtual colonoscopy and fecal occult don’t and can be conducted even without sedation.
How Does the Procedure Work?
Depending on the test, preparation and sedation may be necessary. For sigmoidoscopy and colonoscopy, the bowel should be emptied so the lining becomes clear when viewed. Aside from drinking only liquids at least a day before the exam, enema may also be performed.
During the actual procedure, sedation is provided for patient’s comfort. The scope, which is equipped with a light source and camera, is then inserted into the rectum and to the colon. The camera then sends live feeds of the bowel for proper screening. If there are polyps, they can be removed using small surgical tools.
In double-contrast barium enema, barium is introduced into the body to create contrast in the X-ray. Air is also pumped into the colon so it expands and becomes clearer when tested. This exam doesn’t require any sedation.
In virtual colonoscopy, a scanner that is capable of taking more detailed images of the colon is used. It can rotate around the body while the patient lies on the table.
In fecal occult test, stool samples are collected using a kit that will be provided by the doctor. Depending on the doctor’s instructions, more than one sample may have to be obtained.
Possible Risks and Complications
Some of the exams are performed at different year intervals to minimize the risks, which can include bleeding, which can occur when the lining is irritated. The use of scopes, for example, may also lead to tearing and infection.
The screening tests may also cause discomfort and pain including abdominal cramps, which should disappear gradually.
Itzkowitz SH, Potack J. Colonic polyps and polyposis syndromes. In: Feldman M, Friedman LS, Brandt LJ, eds.Sleisenger and Fordtran's Gastrointestinal and Liver Disease Pathophysiology/Diagnosis/Management.9th ed. Philadelphia, Pa: Elsevier Saunders; 2010:chap 122.
Levin B, Lieberman DA, McFarland B, Smith RA, Brooks D, Andrews KS, et al. Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: a joint guideline from the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA Cancer J Clin. 2008;58:130-160.
National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines): Colorectal cancer screening. Version 2.2013. Available at: http://www.nccn.org/professionals/physiciangls/pdf/colorectalscreening.pdf. Accessed October 24, 2013.
Rex DK, Johnson DA, Anderson JC, Schoenfeld PS, Burke CA, Inadomi JM; American College of Gastroenterology. American College of Gastroenterology