Once breast cancer is diagnosed, it is staged. Staging is a standardized system of classifying the spread and extent of the cancer. According to the American Cancer Society, the stage of the cancer is the most important factor in the choice of treatment and in guiding prognosis. For breast cancer, the stages can run from Stage 0 to Stage 4, in order of ascending severity.
Staging Process
The National Cancer Institute describes several procedures used to help stage breast cancer, including mammograms, biopsies and MRIs. The American Cancer Society lists more tests, such as a PET scan, bone scan, ultrasound and CT scans, that can help identify any spread of the cancer. Based on the results from these tests and findings during surgery, the cancer is staged based on a TNM, or Tumor Node Metastasis system.
T (Tumor)
The T component of the staging describes tumor characteristics. There is a T, followed by a number, which quantifies the size of the tumor and whether it has spread to the skin or chest wall. TX means the tumor cannot be assessed, according to the American Cancer Society. T0 means the primary tumor cannot be seen and Tis describes carcinoma in situ, which means the cancer is noninvasive. T1 is diagnosed when the tumor is 2cm or less; T2 describes a tumor that is between 2cm and 5cm; T3 is a tumor that is more than 5cm; and T4 is a tumor that can be any size but is growing into the skin or the chest wall, including inflammatory breast cancer.
N (Nodes)
N describes the adjacent and nearby lymph node involvement, whether or not there is cancer in the lymph nodes when the cells are examined microscopically. NX means the lymph nodes cannot be examined. This happens in cases in which the nodes have been removed. N0 is diagnosed when nearby lymph nodes are not cancerous. N1 is determined if cancer is in one to three lymph nodes under the arm and/or if small amounts of cancer are found in lymph nodes in the breast near the breastbone. Within N1, there are several sub-stages based on micrometastases and the size of cancer cells in the nodes. N2 is when cancer is in four to nine lymph nodes in the underarm area, or the internal lymph nodes in the breast are swollen. N3 is diagnosed when: cancer is in 10 or more underarm lymph nodes; there is cancer in the nodes under the clavicle; more than 2mm of cancer is found in at least one node under the arm and the mammary nodes are swollen; cancer is in four or more nodes in the armpit and microscopic amounts of cancer are in the mammary lymph nodes; or when at least one node above the clavicle has cancer measuring 2mm or more.
M (Metastasis)
M is the component that describes whether or not there is any metastasis, or spread, of cancer in any distant organs. MX is when the metastases cannot be assessed, and M0 means there is no metastases found on imaging tests or on a physical exam. M1 means there is spread to distant organs, most likely to the brain, bones, lungs or liver.
Stage Grouping
Based on various combinations of TNM, stage grouping is done. This means that each TNM combination corresponds to a specific stage--from Stage 0 (carcinoma in situ) to Stage 4 (metastatic cancer).
