What is Involved in the Staging of Breast Cancer?

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  • Written By: H. Colledge
  • Edited By: Heather Bailey
  • Last Modified Date: 05 September 2019
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Staging of breast cancer is used to describe the size of a breast tumor and the extent to which it has spread. In TNM classification, the letters TNM stand for tumor, node, metastasis. A number is placed after the letter T to represent the size of the tumor, after N to measure any spread to nearby lymph nodes, or glands, and after M to indicate metastasis, or distant spread throughout the body. Another method, the number staging system, assesses tumor size together with the extent of spread, and describes the progression of the disease in four different breast cancer stages, labeled I to IV. Here, stage I represents early breast cancer and stage IV describes the most advanced breast cancer which has spread throughout the body.

Normally, staging of breast cancer is carried out following diagnosis, because it helps doctors decide on the most appropriate treatment. The staging of breast cancer also determines the outlook for an individual. Using the TNM system of staging, a number from 1 to 4 is used to indicate the size of the tumor. T1 represents the smallest tumors and T4 the largest.


The letter N may be followed by a number from 0 to 3. Zero means there is no spread to nearby lymph nodes, N1 indicates that cancer has reached the lymph nodes under the arm, while N2 and N3 represent further levels of spread. M is followed by a number 0 or 1, indicating whether metastasis has occurred or not. During staging of breast cancer the letters and numbers are put together so that, for example, T1 N0 M0 would describe a small tumor with no evidence of spread to lymph nodes or other parts of the body.

When doctors use the number system for staging of breast cancer, stage I breast cancer describes a small tumor which has not spread beyond the breast. Stage II breast cancer indicates either a small tumor, less than 2 inches (around 5 cm) which has spread to nodes under the arm, or a tumor larger than this which has not spread. In stage III breast cancer, a tumor has either spread to numerous lymph nodes or into tissue around the breast and under the arm. Tumors larger than 2 inches (5 cm) can also be classed as stage III even if they have only spread to a few lymph nodes.

Stage IV breast cancer describes metastatic breast cancer, where tumor cells have traveled further in the body to places such as the bones, liver and lungs. Although it is not curable at this level, the cancer may still be treated using radiotherapy, chemotherapy or surgery to reduce symptoms and prolong life. These treatments may also be used in the earlier stages of the disease, where a cure may be possible.



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