Diagnosing Colon Cancer

Diagnosing colon cancer can involve a number of different medical tests and/or procedures. This testing may be done either as regular screening in individuals at risk for colon cancer or may be used to work up a concerning finding or symptoms (such as blood in the stool, etc.). A final diagnosis of colon cancer is only confirmed when tissue from the tumor can be examined by a pathologist who will make the final diagnosis and describe the specific type of tumor and whether it is cancer or not.

Tests and Procedures Used in Diagnosing Colon Cancer:

Fecal Occult Blood Testing: One of the simplest forms of screening for colon cancer is a simple examination of the feces for evidence of hidden blood. Even small amounts of blood that cannot be seen (occult) can be identified. When used regularly after 50 years of age, the presence of blood may help to identify individuals with colon polyps or early cancer. While there are many other things which can cause bleeding in the colon, a positive test can indicate the need for futher work-up, which may lead to diagnosing colon cancer or colon polyps.

Sigmoidoscopy: After thoroughly cleansing the colon, sigmoidoscopy uses a special scope to visually examine the interior of the lower colon and rectum. It can help identify polyps as well as cancerous growths and these can be removed or biopsied through the scope, leading to the diagnosis. It may be used as a screening test or to work-up other findings (symptoms, blood in stool, etc.).

Colonoscopy: Like sigmoidoscopy, colonoscopy can be used as a screening test or to work-up a patient with concerning findings (such as blood in the stool). It also uses a lighted scope to examine the interior of the large intestine and rectum. However, it is a longer flexible scope which can visualize the entire large intestine. Suspicious lesions can also be removed or biopsied through the scope.

Virtual Colonoscopy: A newer form of "colonoscopy", this test uses a CT scanner to produce pictures of the large intestine. It is therefore a less invasive procedure. However, the accuracy in identifying small lesions has not yet been determined. Also, because it is just an image, if a suspicious growth is identified, a second procedure will be required (such as a colonoscopy) to find the lesion and biopsy or remove it.

Barium Enema: This is an X-ray test which uses a barium enema to outline the interior of the colon. This can help identify tumors and polyps. However, it is less accurate at identifying small growths and does not allow biopsy or removal of suspicious lesions.

Digital Rectal Exam: As part of a routine physical examination, a digital rectal exam is performed by a physician who uses their finger to inspect the anus and end part of the rectum for any abnormal masses. Obviously this only allows examination of the very end part of the rectum and therefore is not able to diagnose most cancers or polyps of the colon.

Once one or more of the tests above finds a mass, diagnosing colon cancer requres tissue to be removed or biopsy so that a pathologist can examine it for the presence of cancer. This final colon cancer diagnosis may be made by sigmoidoscopy or colonoscopy since they allow removal of tissue. However, some patients will undergo open surgery to remove suspicious masses which will then be sent to the pathologist.

If a benign polyp is diagnosed, simple removal by colonoscopy is usually sufficient to treat it and prevent that tissue from developing cancer in the future. However, other polyps may appear later, so regular screening is still recommended. If cancer is diagnosed, other treatments (surgery, chemotherapy, radiation, etc.) may be recommended.