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The following staging system is used by a health care team to summarize in a standard way the extent and spread of the cancer. This staging can then be used to determine the treatment most appropriate for the type of cancer.
The most widely used system in the U.S. is the American Joint Committee on Cancer TNM system. A new eighth edition of this staging system has been developed for 2018 that includes results of testing for certain biomarkers, including the HER2 protein and the results of gene expression assays, in addition to the factors (TNM) described below.
Besides the information gained from the imaging tests, this system also uses the results from surgical procedures. After surgery, a pathologist looks at the cells from the breast cancer as well as from the lymph nodes. This information gained is incorporated into the staging as it tends to be more accurate than the physical exam and X-ray findings alone.
TNM staging. This system uses letters and numbers to describe certain tumor characteristics in a uniform manner. This allows health care providers to stage the cancer (which helps determine the most appropriate therapy) and aids communication among health care providers.
T: describes the size of the tumor. It is followed by a number from 0 to 4. Higher numbers indicate a larger tumor or greater spread:
- TX: Primary tumor cannot be assessed
- T0: No evidence of primary tumor
- Tis: Carcinoma in situ
- T1: Tumor is 2 cm or less across
- T2: Tumor is 2 cm-5 cm
- T3: Tumor is more than 5 cm
- T4: Tumor of any size growing into the chest wall or skin.
N: describes the spread to lymph node near the breast. It is followed by a number from 0 to 3.
- NX: Nearby lymph nodes cannot be assessed (for example if they have previously been removed).
- N0: There has been no spread to nearby lymph nodes. In addition to the numbers, this part of the staging is modified by the designation "i+" if the cancer cells are only seen by immunohistochemistry (a special stain) and "mol+" if the cancer could only be found using PCR (special detection technique to detect cancer at the molecular level).
- N1: Cancer has spread to one to three axillary lymph nodes (underarm lymph nodes) or tiny amounts of cancer are found in internal mammary lymph nodes (lymph nodes near breastbone).
- N2: Cancer has spread to four to nine axillary lymph nodes or the cancer has enlarged the internal mammary lymph nodes.
- N3: Any of the conditions below
- Cancer has spread to 10 or more axillary lymph nodes with at least one cancer spread larger than 2 mm.
- Cancer has spread to lymph nodes under the clavicle with at least area of cancer spread greater than 2 mm.
M: This letter is followed by a 0 or 1, indicating whether the cancer has spread to other organs.
- MX: Metastasis cannot be assessed.
- M0: No distant spread is found on imaging procedures or by physical exam.
- M1: Spread to other organs is present.
Once the T, N, and M categories have been determined, they are combined into staging groups. There are five major staging groups, stage 0 to stage IV, which are subdivided into A and B, or A and B and C, depending on the underlying cancer and the T, N, and M scale.
Cancers with similar stages often require similar treatments.
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