If you or a loved one are diagnosed with colon cancer, the first question you’ll ask is: "What stage is it?" Johns Hopkins doctors explain what this important classification means.

If you are diagnosed with colon cancer, your doctor will perform a number of tests to determine the stage of the colon cancer. The stage indicates the extent to which the colon cancer cells have spread within the colon or to other parts of the body and helps your doctor determine the best course of treatment for your colon cancer.

Several different classification systems are used to stage colon cancer, but the most common is the American Joint Committee on Cancer (AJCC) system—also referred to as the TNM system. In this system, the doctor notes the size of the primary colon cancer tumor (T), whether any lymph nodes (N) are affected, and whether the colon cancer has metastasized (M) anywhere else in the body. Based on these findings, the colon cancer is assigned a stage, ranging from Stage 0 (also called carcinoma in situ, in which the colon cancer is contained in the inner lining of the colon) to Stage IV (in which the colon cancer has spread beyond the colon and invaded other organs and tissues in the body).

Several diagnostic tests are used to determine a cancer’s stage, including computed tomography (CT), lymph node biopsy, positron emission tomography (PET), endoscopic ultrasound, magnetic resonance imaging (MRI), and chest x-rays. In some cases, the stage of a cancer cannot be determined until after surgery to remove the tumor. Surgical resection (in which part of the colon or rectum is removed) is the most common treatment for colon cancer and can eliminate the colon cancer in about half of all cases. Chemotherapy and radiation therapy are often needed, as well. These two treatment options can be used either alone or in combination with surgery or each other.

Although other factors—including how healthy you are, whether the colon cancer has narrowed the space within the colon or created a hole in the wall of the colon, and whether the colon cancer is being treated for the first time—affect treatment decisions, treatment for colon cancer depends largely on its stage. The chart below details each of the colon cancer stages and its standard treatment. The size and location of a tumor help determine how it is treated.

• Colon Cancer Stage 0 -- The cancer is confined to the inner lining of the colon. Treatment: Local excision (removal of the tumor without cutting through the abdominal wall) for smaller tumors or surgical resection for larger colon cancer tumors.
• Colon Cancer Stage I -- The cancer has grown through several layers of the colon but has not breached the colon wall. Treatment: Surgical resection of the colon.
• Colon Cancer Stage II -- The cancer has grown beyond the wall of the colon and may be invading nearby tissues, but it has not spread to lymph nodes. Treatment: Surgical resection, plus radiation if your doctor thinks recurrence is likely. Chemotherapy is possible as part of a clinical trial but is not standard treatment for this stage of colon cancer.
• Colon Cancer Stage III -- The cancer has spread to nearby lymph nodes but not to other parts of the body. Treatment: Surgical resection plus chemotherapy. Radiation may be required for large tumors that have spread into nearby tissues.
• Colon Cancer Stage IV -- The cancer has spread to distant organs and tissues (for example, the lung or liver). Treatment: Surgery is palliative, intended to relieve blockage of the colon and other complications rather than cure the cancer. People in poor health may not be good candidates for surgery. Chemotherapy and radiation may also be used to relieve symptoms. Large or numerous metastases may be treated with freezing, microwave therapy, or other methods.