Preventive Health: Colon Cancer Screening

Colon Cancer Screening 

Cancer is the leading cause of death in Singapore. Since 2003, colon cancer has been the most common cancer in males and the second most common cancer in females. Fortunately, colon cancer screening has been shown in studies to be effective in reducing one’s risk of death from this common condition.

Tests that can be used to screen for colon cancer include:

• Stool tests for occult blood
• Stool DNA test
• Colonoscopy
• Computed tomography (CT) colonography

Carcinoembryonic antigen (CEA) is a blood test commonly used to screen for colon cancer. However, this cancer marker does not pick up colon cancer with a high degree of accuracy. In addition, an abnormally high CEA level may be due to causes, other than colon cancer. Hence, the CEA test should not be used as a screening tool.

The stool tests for colon cancer are widely available in primary care clinics and commonly performed. These tests will screen faecal matter for the presence of blood, which is invisible to the naked eye. They include the faecal immunochemical test (FIT) and the Guaiac-based stool test. They are inexpensive and simple to perform. Stool tests will identify individuals with large polyps that are potentially cancerous and colon cancer. Of note, these tests must be performed annually in order to be an accurate screening tool. Two stool samples are required for the FIT and three stool samples are recommended for the Guaiac-based stool test.

Another test is the stool DNA test. This is a recently developed test, which screens faecal matter for DNA mutations and biomarkers that are associated with colon cancer. Only one stool sample is required and it should be repeated once every three years. Of all these stool tests, the FIT is the most readily available and commonly used one.

Colonoscopy is another test frequently performed to screen for colon cancer. It involves passing a thin flexible tube with a camera at its end, into the anus. The scope is then used to examine the large intestine. The colon requires cleansing with a special laxative in order to perform this procedure. Proper bowel cleansing is important because it ensures that the test is accurate. Poor bowel preparation will result in small polyps being missed. This procedure is performed under sedation so that there is no discomfort to the individual. An advantage of colonoscopy over the other tests is that it can detect small polyps with a high degree of accuracy, and remove or biopsy any suspicious lesions. Hence, colonoscopy not only screens for colon cancer, it can also prevent cancer by removing polyps from the colon.

CT colonography is another test that can screen for colon cancer. Patients are given a laxative to cleanse their large intestine, before the procedure. During the test, air or carbon dioxide is gradually introduced into the rectum to distend the colon. After that, a CT scanner is used to capture multiple images of the large intestine. Unlike colonoscopy, CT colonography does not require any sedation. Another advantage of CT colonography is that other organs within the abdomen can be examined as well. Individuals who undergo this test will be exposed to small doses of radiation. Hence, undergoing multiple CT colonography tests as part of a screening protocol will lead to increasing levels of radiation exposure.