After colon cancer is diagnosed, tests are performed to determine if the cancer has spread in the colon or spread to other parts of the body.
The procedure to check whether the cancer has spread in the colon or has spread to other parts of the body is called staging. The information obtained during the staging process determines the stage of the disease. It is important to know the staging in order to develop a treatment plan.
The following tests and procedures may be used during staging:
CT scan (CAT scan): A procedure in which a series of detailed pictures are taken of the inside of the body, such as the abdomen, pelvis, and chest, from different angles. The pictures are generated by a computer connected to an x-ray machine. Dye may be injected into a vein or swallowed and used to help organs or tissues show up more clearly. This procedure may be called computed tomography, computerized tomographic imaging, or computerized axial tomography.
MRI (magnetic resonance imaging): This procedure uses a magnet, radio waves, and a computer to take a series of detailed pictures of the inside of the colon. A substance called gadolinium is injected into the patient’s body through a vein. The gadolinium collects around the cancer cells, making them appear brighter in the pictures. This procedure is also known as magnetic resonance imaging (NMRI).
PET scan (positron emission tomography): A procedure used to find tumor cells in the body. A small amount of radioactive glucose (sugar) is injected into a vein. a PET scanner surrounds the body to take pictures of where the glucose is used in the body. Malignant tumor cells are brighter in the picture because they are more active and take up more glucose than normal cells.
X-ray chest x-ray: An x-ray camera that targets the organs and bones in the chest. x-rays are beams of energy that shoot through the body to the bottom of the film, creating an image of the inside of the body.
Surgery: This is a procedure to remove a tumor and see how it has spread in the colon.
Lymph node biopsy: All or part of a lymph node is removed. The pathologist looks at the lymph node tissue under a microscope to check for cancer cells. This can be done during surgery or a fine-needle aspiration biopsy can be performed under ultrasound endoscopic guidance.
Complete blood count (CBC): A procedure in which a blood sample is collected and examined for the following parameters.
Red blood cell, white blood cell, and platelet counts.
The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.
The portion of the blood sample that is composed of red blood cells.
Carcinoembryonic antigen (CEA) assay: A test that measures the level of CEA in the blood. cEA is released into the blood from cancer cells and normal cells. When CEA is higher than normal amounts, this may be a sign of colon cancer or other disease.
Cancer cells spread through the body in three ways.
Cancer cells can spread through the tissues, lymphatic system, and blood:
Tissues: Cancer cells spread by growing from the site where they started to the neighboring sites.
Lymphatic system: Cancer cells spread from entering the lymphatic system. Cancer cells move through the lymphatic vessels to other parts of the body.
Blood: Cancer cells spread from entering the bloodstream. Cancer cells travel through blood vessels to other parts of the body.
Cancer cells may spread from where they started to other parts of the body.
When cancer cells spread to another part of the body, it is called metastasis. The cancer cells break away from where they started (the primary tumor) and travel through the lymphatic system or bloodstream.
Lymphatic system: Cancer cells enter the lymphatic system, move through the lymphatic vessels, and form tumors elsewhere in the body (metastases).
Blood: Cancer cells enter the bloodstream, metastasize through blood vessels, and form tumors elsewhere in the body (metastases).
Metastases are the same type of tumor as the primary tumor. For example, if colon cancer spreads to the lungs, the cancer cells in the lungs are actually colon cancer cells. The disease is metastatic colon cancer, not lung cancer.
Many people with cancer die because the cancer cells have metastasized and spread from the original tumor to other tissues and organs. This is called metastatic cancer. This animation shows how cancer cells migrate from where they first formed in the body to other parts of the body.
Colon cancer is staged as follows:
Stage 0 (carcinoma in situ)
Stage 0 (colon cancer in situ). The abnormal cells are located in the mucosa of the colonic wall.
In stage 0, abnormal cells are found in the mucosa of the colon wall (innermost layer). These abnormal cells may become cancerous and spread to nearby normal tissue. stage 0 is also called carcinoma in situ.
Stage I
Stage I colon cancer. Cancer cells have spread from the mucosa of the colon wall to the submucosa or muscle layer.
In stage I colon cancer, cancer cells have formed in the mucosal layer (the innermost layer) of the colon wall and have spread to the submucosa (the layer of tissue next to the mucosa) or the muscularis layer of the colon wall.
Stage II
Stage II colon cancer. In stage IIA, cancer cells have spread through the muscular layer of the colon wall to the plasma membrane. In stage IIB, cancer cells have spread through the plasma membrane but not to adjacent organs. In stage IIC, the tumor has spread through the plasma membrane to nearby organs.
Stage II colon cancer is divided into stage IIA, stage IIB, and stage IIC.
Stage IIA: The cancer has spread through the muscular layer of the colon wall to the plasma membrane (the outermost layer) of the colon wall.
Stage IIB: Cancer cells have spread through the plasma membrane (outermost layer) of the colon wall to the tissues surrounding the abdominal organs (visceral peritoneum).
Stage IIC: Cancer cells have passed through the plasma membrane (outermost layer) of the colon wall and spread to nearby organs.
Stage III
Stage III colon cancer is classified as stage IIIA, stage IIIB, and stage IIIC.
Stage IIIA colon cancer. The cancer has spread through the mucosa of the colon wall to the submucosa, may have spread to the muscularis, and has spread to one to three nearby lymph nodes or tissue adjacent to the lymph nodes. Alternatively, cancer cells have spread through the mucosal layer to the submucosa and to 4 to 6 nearby lymph nodes.
In stage IIIA, the cancer has spread:
through the mucosal layer (innermost layer) of the colonic wall to the submucosa (layer of tissue next to the mucosa) or to the muscular layer of the colonic wall. Cancer cells have spread to one to three nearby lymph nodes, or have formed in the tissues near the lymph nodes; or
through the mucosal layer (innermost layer) of the colon wall to the submucosal layer (layer of tissue near the mucosa). The cancer has spread to four to six nearby lymph nodes. 
Stage IIIB colon cancer. Cancer cells have spread through the muscular layer of the colon wall to the plasma membrane, or have spread through the plasma membrane but not to adjacent organs; cancer cells have spread to one to three nearby lymph nodes or tissues near the lymph nodes. Alternatively, the cancer cells have spread to the muscularis or plasma membrane and to 4 to 6 nearby lymph nodes. Alternatively, cancer cells have spread through the mucosal layer to the submucosal layer and may have spread to the muscularis; cancer cells have spread to 7 or more nearby lymph nodes.
In stage IIIB, the cancer has spread:
through the muscular layer of the colonic wall to the plasma membrane of the colonic wall (outermost layer) or through the plasma membrane to the tissues of the abdominal organs (visceral peritoneum). Cancer cells have spread to one to three nearby lymph nodes or have formed in the tissues near the lymph nodes; or
to the muscularis or plasma membrane (outermost layer) of the colonic wall. The cancer has spread to 4 to 6 nearby lymph nodes; or
through the mucosal layer (innermost layer) of the colon wall to the submucosa (layer of tissue next to the mucosa) or to the muscular layer of the colon wall. The cancer has spread to 7 or more nearby lymph nodes. 
Stage IIIC colon cancer. The cancer has spread through the plasma membrane of the colon wall but has not spread to nearby organs; the cancer has spread to four to six nearby lymph nodes. Alternatively, the cancer has spread through the muscularis to the plasma membrane, or has spread through the plasma membrane but not to nearby organs; the cancer has spread to 7 or more nearby lymph nodes. Alternatively, cancer cells have spread through the plasma membrane to nearby organs and to 1 or more nearby lymph nodes or tissues near lymph nodes.
In stage IIIC, the cancer has spread:
through the plasma membrane of the colonic wall (outermost layer) to the tissues of the abdominal organs (visceral peritoneum). The cancer has spread to 4 to 6 nearby lymph nodes; or
Reaching the plasma membrane of the colon wall (outermost layer) through the muscular layer of the colon wall or reaching the tissues of the abdominal organs through the plasma membrane (visceral peritoneum). Cancer cells have spread to 7 or more nearby lymph nodes; or
Reaching nearby organs through the plasma membrane (outermost layer) of the colon wall. Cancer cells have spread to 1 or more nearby lymph nodes, or have formed in the tissue near the lymph nodes.
Stage IV
Stage IV colon cancer. The cancer has spread through the blood and lymph nodes to other parts of the body, such as the lungs, liver, abdominal wall, or ovaries.
Stage IV colon cancer is divided into stages IVA, IVB, and IVC.
Stage IVA: The cancer has spread to an area or organ not near the colon, such as the liver, lungs, ovaries, or distant lymph nodes.
Stage IVB: The cancer has spread to multiple areas or organs near the non-colon, such as the liver, lungs, ovaries, or distant lymph nodes.
Stage IVC: The cancer has spread to the tissues surrounding the abdominal wall and may have spread to other areas or organs.