Stages of Breast Cancer: What do they mean?
There are five stages of breast cancer, starting with stage 0, or noninvasive cancer, and concluding with stage four, or metastatic breast cancer. There are two types of staging; anatomic and prognostic. Anatomic staging uses the TNM (tumor, node, and metastasis) system. The new AJCC 8th Edition Staging system considers both anatomic staging and prognostic staging, which takes genomic testing, grade (what the cancer cells look like under the microscope), and receptor status (ER/PR/HER2) into consideration.
Anatomic Staging
T: T stands for Tumor size, measured in centimeters.
T1: <2cm
T2: 2-5cm
T3: >5cm
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N: N stands for Number of lymph nodes that your cancer has spread to.
N1: 1-3 lymph nodes
N2: 4-9 lymph nodes
N3: 10+ lymph nodes
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M: M stands for Metastasis, or whether your cancer has spread to other organs. If your cancer has spread at all, it is immediately classified as stage four.
M0: cancer has not metastasized
M1: cancer has metastasized
Stage 0 or In Situ Cancer
Stage 0 breast cancer is noninvasive, meaning that it exists only in the ducts or lobules and has not yet spread into the surrounding tissue. Therefore, the cancer currently has no way to spread, as it does not have access to the lymphatic system or the bloodstream. However, stage 0 breast cancer has a risk or developing into a later stage cancer, meaning that it will most likely need to be treated, usually by surgery coupled with hormone or targeted therapy.
Stage 1 Breast Cancer
Stage 1 breast cancer is the first stage of invasive breast cancer. The cancer is no longer contained the ducts or lobules, and therefore has the potential to spread through the lymphatic system or the bloodstream. Stage I breast cancer can be classified into two subtypes:
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Stage IA:
The tumor is very small and has not yet spread to any lymph nodes. (T1, N0, M0)
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Stage IB: The tumor has spread to a small number of lymph nodes and is less than 2cm in size. (T0 N1 M0 or T1 N1 M0).
Stage 2 Breast Cancer
Stage 2 breast cancer is an invasive cancer. In this case, your tumor may be larger than 2cm and/or may have spread to nearby axillary lymph nodes (lymph nodes in the armpit that drain lymph from the breast).
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Stage IIA: There is no tumor in the breast or there is a tumor 2cm or smaller, but there are cancerous cells in 1-3 axillary lymph nodes (T0/1, N1, M0).
OR
There is a 2 to 5cm tumor in the breast but the cancer has not spread to any lymph nodes. (T2, NO, M0)
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Stage IIB: The tumor is 2 to 5cm and has spread to 1 to 3 lymph nodes (T2, N1, M0)
OR
There is a tumor larger than 5cm but the cancer has not spread to any axillary lymph nodes. (T3, N0, M0)
Stage 3 Breast Cancer
Stage three breast cancer is an invasive breast cancer, meaning that it is no longer contained to the ducts or lobules and has infiltrated the breast tissue.
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Stage IIIA: A tumor of any size has spread to 4 to 9 lymph nodes (any T, N2, M0)
OR
The tumor is larger than 5cm and has spread to 1 to 3 lymph nodes (T3, N1, M0).
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Stage IIIB: A tumor is any size and has spread to the wall of the chest and up to 9 lymph nodes. (any T, N1 or N2, M0) Stage IIIB breast cancer has the potential to cause swelling of the breast.
Inflammatory breast cancer is automatically considered stage IIIB breast cancer (or greater, depending on if the cancer has metastasized).
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Stage IIIC: The tumor may be any size and has spread to more than ten lymph nodes (any T, N3, M0).
Stage 4 (Metastatic) Breast Cancer
Stage four breast cancer, also known as metastatic breast cancer, is the highest stage of breast cancer. No matter the size of the tumor, your cancer is stage four if it has spread to at least one other organ or tissue, such as the liver, bones, lungs, etc.
(any T, any N, M1).
Prognostic Staging
Prognostic staging includes the TNM system, but also takes genomic tests, the cancer grade, and the cancer receptor status into consideration.
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Genomic Tests
Genomic Tests are tests that look at your entire genome in order to identify genetic mutations in your cancer. Genomic tests also provide a cancer risk or recurrence score, which can help determine how your cancer will behave, and how it will respond to certain treatments. If your cancer has a lower recurrence score, it may be classified as a lower stage than a cancer with the same TNM with a higher recurrence score. (Genomic testing is different than genetic testing, which looks for hereditary mutations such as BCRA 1 and 2 that increase your risk of cancer). Common genomic tests include oncotype DX, mammaprint, endopredict, PAM 50, and the Breast Cancer Index.
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Grade
Cancer grade is how cancer cells look under the microscope compared to normal cells. There are three main degrees of differentiation that are used to determine grade, which in turn can help determine how fast your cancer will spread.
1) Grade 1 or Well-differentiated: well-differentiated cells resemble normal, healthy breast cells. Grade 1 cancers are not as aggressive and spread slower than higher grade cancers.
2) Grade 2 or Moderately differentiated: these cells look more abnormal that Grade 1 cells, but less abnormal than higher grade cells. Therefore, they are moderately aggressive and spread at a moderate rate compared to the other two grades.
3) Grade 3 or Well Differentiated Cells: Well differentiated cells are "ugly" cancer cells that do not resemble normal breast tissue cells. These cells have the potential to replicate and spread very quickly.
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Receptor Status
Receptor status classifies cancer based on its molecular subtype, or, in other words, its biomarkers. The three common biomarkers for breast cancer are ER, PR, and HER2.
If your cancer is ER, PR, or HER2 positive, it is easier to treat because there are many systemic therapy options (hormone therapy, targeted therapy, chemotherapy, etc). Therefore, your stage will most likely be lower in the prognostic staging system than someone with TNBC (ER/PR/HER2-).
However, if your cancer is triple negative (TNBC), meaining that it does not express ER, PR, or HER2, it will be harder to treat since there are not as many systemic therapies available as there are for ER, PR, or HER2 positive cancers. Therefore, your stage will most likely be higher in the prognostic staging system.
To learn more about cancer biomarkers, or molecular subtypes, click here.
To learn more about treatment options specific to your cancer, click on types of cancer in the website menu.