If the biopsy shows that cancer is present, your doctor needs to know the extent (stage) of the disease to plan the best treatment. The stage is based on whether the tumor has invaded nearby tissues, whether the cancer has spread and, if so, to what parts of the body.

Your doctor may order some of the following tests:

• Blood tests: Your doctor checks for carcinoembryonic antigen (CEA) and other substances in the blood. Some people who have colorectal cancer or other conditions have a high CEA level.

• Colonoscopy: If colonoscopy was not performed for diagnosis, your doctor checks for abnormal areas along the entire length of the colon and rectum with a colonoscope.

• Endorectal ultrasound: An ultrasound probe is inserted into your rectum. The probe sends out sound waves that people cannot hear. The waves bounce off your rectum and nearby tissues, and a computer uses the echoes to create a picture. The picture may show how deep a rectal tumor has grown or whether the cancer has spread to lymph nodes or other nearby tissues.

• Chest x-ray: X-rays of your chest may show whether cancer has spread to your lungs.

• CT scan: An x-ray machine linked to a computer takes a series of detailed pictures of areas inside your body. You may receive an injection of dye. A CT scan may show whether cancer has spread to the liver, lungs, or other organs.

Your doctor may also use other tests (such as MRI) to see whether the cancer has spread. Sometimes staging is not complete until after surgery to remove the tumor. (Surgery for colorectal cancer is described in the "Treatment" ¹ section.)

Doctors describe colorectal cancer by the following stages:

Glossary Terms

A substance that is sometimes found in an increased amount in the blood of people who have certain cancers, other diseases, or who smoke. It is used as a tumor marker for colorectal cancer. Also called carcinoembryonic antigen.

A series of detailed pictures of areas inside the body taken from different angles. The pictures are created by a computer linked to an x-ray machine. Also called CAT scan, computed tomography scan, computerized axial tomography scan, and computerized tomography.

A procedure in which an endoscope is inserted into the body. An endoscope is a thin, tube-like instrument that has a light and a lens for viewing. A probe at the end of the endoscope is used to bounce high-energy sound waves (ultrasound) off internal organs to make a picture (sonogram). Also called endosonography and EUS.

A procedure in which radio waves and a powerful magnet linked to a computer is used to create detailed pictures of areas inside the body. These pictures can show the difference between normal and diseased tissue. MRI makes better images of organs and soft tissue than other scanning techniques, such as computed tomography (CT) or x-ray. MRI is especially useful for imaging the brain, the spine, the soft tissue of joints, and the inside of bones. Also called magnetic resonance imaging, NMRI, and nuclear magnetic resonance imaging.

The extent of a cancer in the body. Staging is usually based on the size of the tumor, whether lymph nodes contain cancer, and whether the cancer has spread from the original site to other parts of the body.