Colon Cancer Tests and Diagnoses

If you are experiencing any signs or symptoms that could indicate cancer, your doctor will do a physical exam and discuss your medical history. In addition, your doctor may order other tests and exams. These may include imaging procedures, endoscopy and/or laboratory tests. Your doctor may also order a biopsy. 

With proper screening, colon cancer can be detected before symptoms develop, when it is most curable. The following screening modalities are recommended due to their ability to spot both colorectal polyps (a potential precursor to cancer), as well as cancer:

  • Flexible sigmoidoscopy performed every five years.
  • Colonoscopy performed every 10 years. These first two tests involve a flexible tube tipped with a small camera; polyps can be removed upon discovery. With colonoscopy, doctors view the entire length of the colon, while sigmoidoscopy views only the lower one-third.
  • Double contrast barium enema every five years. With this test, a barium-laden liquid is admitted into the colon via catheter. X-rays are then used to spot abnormalities.
  • Computed tomography (CT) colonography (virtual colonoscopy) every five years. In this test, the colon is first widened with air, then CT scanning helps pick up polyps or cancer.

A fecal occult blood test (FOBT) may detect small amounts of blood in the stool, which could suggest colon cancer. However, this test is often negative in patients with colon cancer. For this reason, a FOBT must be done along with colonoscopy or sigmoidoscopy. It is also important to note that a positive FOBT doesn't necessarily mean a cancer diagnosis.

If it is determined that a patient does indeed have colorectal cancer, more tests will be performed to see if the cancer has spread. This is called staging. CT or magnetic resonance imaging (MRI) scans of the abdomen, pelvic area, chest or brain may be used to stage the cancer. On some occasions, positron emission tomography (PET) scans are also used.

Stages of colon cancer are:

  • Stage 0: Very early cancer on the innermost layer of the intestine
  • Stage I: Cancer is in the inner layers of the colon
  • Stage II: Cancer has spread through the muscle wall of the colon
  • Stage III: Cancer has spread to the lymph nodes
  • Stage IV: Cancer has spread to other organs