Breast cancer staging is determined by the size of the cancer as well as how far it has spread. Breast cancer staging is necessary for a doctor to understand how far the cancer has progressed within the body.
Knowing which stage the cancer is in will also determine the course of action and the treatment plan that needs to be followed. There are two types of staging systems that are commonly used in breast cancer staging – the number staging system and the TNM staging system.
Number Staging System
There are 4 stages in the number staging system of breast cancer. These are stage I, stage II, stage III and stage IV – depending on the size and the progression of the cancer.
This is the first stage of breast cancer. The cancer is still very small and measures less than, equal to, but not more than 2 cm. It is still localized and has not progressed to the other parts of the body. The axillary lymph nodes (the lymph nodes that are present in the armpits) are clear and devoid of cancer.
The second stage of cancer can be classified into IIA and IIB. In stage IIA of breast cancer staging there are three possibilities: The cancer is less than 2 cm but has spread to the axillary lymph nodes, is greater than 2 cm but less than 5 cm but has not spread to the axillary lymph nodes, or there is no sign of the disease in the breast but there is sign of cancer in the axillary lymph nodes. In stage IIB the cancer is either less than 5 cm and has spread to the axillary lymph nodes or it is larger than 5 cm but is localized.
This stage can be classified into IIIA, IIIB and IIIC. In stage IIIA the cancer is either less than 5 cm or more than 5 cm but in both cases it has spread to the axillary lymph nodes. Stage IIIB has the cancer spreading to the breast tissue. Traces of cancer cells are noticed in the axillary lymph nodes as well.
The adjoining muscle and skin may or may not be involved. In Stage IIIC the cancer has definitely spread to the axillary lymph nodes, the breastbone and collarbone.
The cancer has spread to other organs such as the liver, lungs and even to the bones. At this stage the cancer is known as metastatic breast cancer.
TNM Staging System
TNM is the letter staging system of breast cancer. TNM stands for tumor (T), lymph nodes (N) and metastasis (M). T refers to the size of the tumor and can be classified as T1, T2, T3 or T4 depending on the size of the tumor. N refers to the involvement of the lymph nodes and the number of lymph nodes that are involved.
M describes the extent to which metastasis has progressed where MX refers to metastasis that cannot be assessed, MO refers to no metastasis and M1 refers to metastasis that is present.