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Staging is the process of finding out how widespread the cancer is when it is found. The stage of a cancer is the most important factor in choosing among treatment options. The stage is based on whether the cancer is invasive or non-invasive, the size of the tumor, how many lymph nodes are involved, and whether it has spread to other parts of the body.

The TNM staging system

The most common system used to describe the stages of breast cancer is the AJCC/TNM system. This system takes into account the tumor size and spread (T), whether the cancer has spread to lymph nodes (N), and whether it has spread to distant organs (M, for metastasis). Numbers after the T, N, and M give details about the cancer.

All of this information is combined in a process called stage grouping. The stage is then expressed as a Roman numeral. After stage 0 (carcinoma in situ), the other stages are I through IV (1-4). Some of the stages are further divided into sub stages using the letters A, B, and C. As a rule, the lower the number, the less the cancer has spread. A higher number, such as stage IV (4), means a more advanced cancer. And within a stage, an earlier letter means a lower (and often better) stage. Cancers with similar stages tend to have a similar outlook and are often treated in much the same way.

After looking at your test results, the doctor will tell you the stage of your cancer. Breast cancer staging can be complex. Be sure to ask your doctor to explain your stage in a way you understand. This will help you both decide on the best treatment for you.

Last Medical Review: 09/09/2014
Last Revised: 01/14/2016