Gastrointestinal (GI) Oncology Program

Colon Cancer

Screening and Diagnosis

Routine screening tests are recommended for patients who have any of the risk factors, which are outlined in Symptoms.

A doctor may also order these tests to look for cancer if a patient experiences a change in bowel habits or bleeding from the rectum.

The three screening and diagnostic tests performed most commonly for colon cancer are the following:

Rectal examination: Wearing thin gloves, the doctor puts a greased finger into the rectum and gently feels for lumps. The doctor might also check material collected from the rectum to see if there is any blood in it.
Proctoscopy: The doctor might want to look inside the rectum and lower colon with a special instrument called a sigmoidoscope or a proctosigmoidoscope. This examination, called a proctoscopy or procto examination, finds about half of all colon and rectal cancers. The test is usually done in a doctor’s office. The patient usually will feel some pressure but usually does not feel pain.
Colonoscopy: The doctor might also want to look inside the rectum and the entire colon with a special tool called a colonoscope. This test can also be done in a doctor’s office. It too causes some pressure, but usually it does not cause the patient to feel pain. (See article on Virtual Colonoscopy, or CT colonography, for more information.)

If, when doing these tests, the doctor finds tissue that is not normal, he or she will need to cut out a small piece of the tissue and look at it under a microscope to see if it contains any cancer cells. This procedure is called a biopsy and is usually done in the doctor’s office during the proctoscopy or colonoscopy.

The prognosis (chance of recovery) from colon cancer and the choice of treatment for the disease depend on the stage of the cancer (whether it is just in the inner lining of the colon or has spread to other places) and the patient’s general health.

After treatment, the patient will usually have a blood test (to measure amounts of carcinoembryonic antigen or CEA in the blood) and x-rays to see if the cancer has come back.

This page was last updated on: March 3, 2008.

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