Staging is the process of describing a cancer, such as where it is located, if or where it has spread, and if it is affecting the functions of other organs in the body. Doctors use diagnostic tests to determine the cancer's stage, so staging may not be complete until all of the tests are finished. Knowing the stage helps the doctor to decide what kind of treatment is best and can help predict a patient's prognosis (chance of recovery). There are different stage descriptions for different types of cancer.

A number of different staging systems are currently used; the most common is the TNM staging system, as proposed by the American Joint Committee on Cancer (AJCC). TNM is an abbreviation for tumor (T), node (N), and metastasis (M). Doctors look at these three factors to determine the stage of cancer:

• How large is the primary tumor and where is it located? (Tumor, T)
• Has the tumor spread to the lymph nodes? (Node, N)
• Has the cancer metastasized (spread) to other parts of the body? (Metastasis, M)

The results are combined to determine the stage of cancer for each person. Stages are written as Roman numerals one through four (I, II, III, or IV). A person may be diagnosed with stage zero (stage 0) cancer, which means the cancer is confined to the place where it started and has not invaded any surrounding areas. Stage 0 cancer is also called cancer in situ. One example is ductal carcinoma in situ (DCIS) of the breast, which is breast cancer that has not spread to outside of the duct of the breast.

A cancer with a lower stage is usually associated with a better prognosis; however, staging cannot be used to predict how long someone will live with cancer. Staging only provides a way of organizing information about a person's cancer so that doctors can better evaluate the treatment options. Find specific information about staging for each cancer type.