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Colon Cancer Diagnosis

The following tests may be used to diagnose colon cancer or find out if it has spread. Tests also may be used to find out if surrounding tissues or organs have been damaged by treatment.

Digital rectal exam (DRE): The doctor inserts a gloved finger into the rectum to feel for polyps or other problems.

Fecal occult blood test (FOBT): This take-home test finds blood in stool.

Fecal immunochemical test (FIT): This take-home test finds blood proteins in stool.

Endoscopic tests, which may include:

  • Sigmoidoscopy: A tiny camera on flexible plastic tubing (sigmoidoscope) is inserted into the rectum. This gives the doctor a view of the rectum and lower colon. Tissue or polyps can be removed and looked at under a microscope.
  • Colonoscopy: A longer version of a sigmoidoscope, a colonscope can look at the entire colon.

Endoscopic ultrasound (EUS): An endoscope is inserted into the rectum. A probe at the end bounces high-energy sound waves (ultrasound) off internal organs to make a picture (sonogram). Also called endosonography.

Imaging tests, which may include:

  • CT or CAT (computed axial tomography) scan
  • MRI (magnetic resonance imaging) scan
  • PET/CT (positron emission tomography) scan
  • Virtual colonoscopy or CT (computed tomography) colonoscopy
  • Double contrast barium enema (DCBE): Barium is a chemical that allows the bowel lining to show up on an X-ray. A barium solution is given by enema, and then a series of X-rays are taken.

Blood test for carcinoembryonic antigen (CEA): CEA is a protein, or tumor marker, made by some cancerous tumors. This test also can be used to find out if the tumor is growing or has come back after treatment.

Colon Cancer Staging

If you are diagnosed with colon cancer, your doctor will determine the stage of the disease. Staging is a way of classifying cancer by how much disease is in the body and where it has spread when it is diagnosed. This helps the doctor plan the best way to treat the cancer. Once the staging classification is determined, it stays the same even if treatment works or the cancer spreads.

Colon Cancer Stages

(Source: National Cancer Institute)

Stage 0: Abnormal cells are found in the inner lining of the colon. These abnormal cells may become cancer and spread into nearby normal tissue. Stage 0 also is called carcinoma in situ.

Stage I: Cancer has formed and spread into the first (submucosa) or second (muscle) layers of the rectal wall. It has not spread outside of the rectum.

Stage II: Cancer has spread outside of the rectal walls into the surrounding fat or nearby tissue. It has not gone into the lymph nodes.  It is divided into stages IIA, IIB or IIC depending on the extent of local tumor involvement.

Stage III: Cancer has spread to nearby lymph nodes. It has not spread to other parts of the body.  It is divided into stages IIIA, IIIB or IIIC depending on the extent of local tumor involvement and the number of lymph nodes that contain cancer.

Stage IV: Cancer has spread to other parts of the body, such as the liver, lungs or ovaries. It is divided into stages IVA and IVB depending on the number of different other parts of the body to which the cancer has spread.

Stage IV: Cancer may have spread to nearby lymph nodes and has spread to other parts of the body, such as the liver or lungs.

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Knowledge Center

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