Staging indicates the location of cancer, the extent of its growth, if it has reached different parts of the body, and which parts of the body it has spread to. Classifying breast cancer using the TNM staging system is key in helping the doctor understand which treatment option is right at that point in time and can improve the chances of recovery. Let’s review aspects of the TNM staging system for breast cancer:

1. What does TNM stand for?

• T (Tumor): What is the size of the tumor and where is it present?
• N (Node): Did the tumor extends to the lymph nodes? What is the location of the affected lymph nodes and how many have been affected?
• M (Metastasis): Did other parts of the body get affected by cancer? Which parts have been affected and by how much extent?

2. Tumor stage

A combination of answers to all the above questions is used to indicate and differentiate between the stages of breast cancer. Staging could be clinical or pathological. Clinical staging provides information through tests performed before the surgery while pathological staging provides the information found during the surgery being performed. It gives the doctor pertinent information to determine the patient’s prognosis. The tumor (T) stage, on the basis of its location and size, is explained as follows:

• TX: The tumor cannot yet be evaluated.
• T0: Lack of any evidence of cancer in the breast.
• Tis: Indicates carcinoma in-situ. This indicates that the cancer is located in the lobules of the breast tissue and hasn’t yet spread beyond the layer of the tissue.
• T1: The size of the tumor is 20mm or smaller at its widest region. This is further classified into T1mi, T1a, T1b, T1c on the basis of the size of the tumor.
• T2: The size of the tumor lies in between 20mm and 50mm.
• T3: The size of the tumor is greater than 50mm.
• T4: Tumor growth has extended into different parts with T4a referring to the chest wall, T4b—the skin, T4c referring to chest wall and skin, and T4d meaning inflammatory breast cancer

3. Node (N) stage

• NX: Lymph nodes have not been evaluated
• N0: Either no cancer was found or areas of cancer found were smaller than 0.2mm.
• N1: Cancer has either extended into 1-3 axillary lymph nodes or internal mammary lymph nodes or both.
• N2: Cancer has either extended into 4-9 axillary lymph nodes or internal mammary lymph nodes.
• N3: cancer has extended to 10 or more axillary lymph nodes. It could have also spread to the lymph nodes under the collar bone, internal mammary lymph nodes, or the ones above the clavicle.

4. Metastasis (M) stage

• MX: No distant spreading has been evaluated.
• M0: Cancer has not metastasized.
• M0 (i+): While no evidence of distant metastases has been found through radiographic or clinical tests, microscopic evidence of tumor cells has been observed in the bone marrow, blood, or other lymph nodes with a size smaller than 0.2mm.
• M1: Breast cancer has spread to other parts of the body and there is evidence of this metastasis.