Most colon cancers begin as polyps which are growths that line the colon. In most cases these polyps are benign or non-cancerous growths but can later turn into cancer. Polyps can be of the raised or flat type. Raised polyps grow on the inner surface of the colon like mushrooms without the stocks. In people older than the age of 50, polyps are common. Polyps are not cancerous but certain type of polyps known as adenoma may have a higher risk of turning into cancer.
Several screening systems have been developed to help doctors identify polyps and remove them in the process. Screening for colon cancer is not only a method of testing and identifying, but can also be seen as way of preventing colon cancer from occurring.
What are the different screening systems used for colon cancer?
High sensitivity fecal occult blood test (FOBT):
This type of screening system is a blood test that checks for blood in the feces as colon cancer can cause bleeding. There are two types fecal occult blood tests, guaiac fecal occult blood test and the fecal immunochemical test.
The guaiac fecal occult blood test (gFOBT) uses a specific chemical to identify heme, which is a blood protein that is found in hemoglobin. For this test there are dietary restrictions that should be followed before taking the test as the chemical used in the test can identify heme in some food like red meat.
The fecal immunochemical test (FIT) uses antibodies to detect hemoglobin. There are no dietary restrictions to be followed before taking this test.
Standard or optical colonoscopy
In this screening system, the entire colon is examined using a colonoscope which is a flexible tube which has tool for viewing and removing required tissue. Thorough cleansing of the colon is required before the test. The colonoscope is inserted through the anus and into the rectum and colon and carbon dioxide is pumped into the lining of the colon so that the doctor can view the lining of the colon a lot more easily. Abnormal growths like polyps can be removed during a colonoscopy. Doctors recommend doing a colonoscopy every 10 years for people at average risk as long as test results come out negative.
A sigmoidoscopy uses a flexible light tube which is inserted to visualise the rectum and sigmoid colon. A thorough cleansing of the lower colon is required before the test.It has a lens for viewing and a tool for removing tissue. This tube is inserted through the anus and into the rectum and carbon dioxide is pumped so that the doctor can view the lining of the colon a lot more easily. Abnormal growths in the colon are removed during a sigmoidoscopy and are taken for analysis.
Also known as computed tomographic (CT) colonography, this system of screening uses a CT scanner which produces a series of pictures of the colon from outside the body. A computer is then used to assemble these pictures into detailed images. A virtual colonoscopy can show details of abnormal growths like polyps and just like the standard colonoscopy carbon dioxide is pumped into the colon to expand it for better viewing. During this method, the person does not require to be sedated and a virtual colonoscopy has less complications.