The size of a breast tumor can give healthcare providers a sense of the severity of a case of breast cancer, but staging that cancer by considering this information along with lymph node status and metastasis is essential to determining the extent of disease, treatment options, and prognosis.
Right now, there is not a simple test that can determine all of this and, moreover, what these factors—in combination—mean for a patient. Rather, healthcare providers use the TNM Staging System, developed by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC), to conclude how these three characteristics together define a case of breast cancer. You will be told the stage of your breast cancer at some point in your cancer journey, especially after you’ve had a breast biopsy, lumpectomy, or mastectomy.
The TNM System for Breast Cancer Staging
TNM is the most widely used staging system for breast cancer. Each letter of the acronym stands for a defining element of the disease.
To measure the size of your tumor before surgery, healthcare providers rely on imaging studies.
Standard breast imaging methods include:
- Mammogram: Traditional film mammography can be used to image breast tissue. If you are post-menopausal, have fatty breast tissue, or have been pregnant, this may be accurate enough. If you have dense breast tissue, digital mammography is more reliable.
- Breast ultrasound: Ultrasound can be used to make a measurement of a breast tumor, but it has been found to underestimate tumor size and is considered less accurate than mammography.
- Breast MRI: While a mammogram may find your lump, an MRI might be needed to measure it if your breast tissue is dense or your biopsy shows that the mass is larger than expected. However, while MRI can create a clear image of your tumor, it tends to overestimate the actual size in three dimensions.
After reviewing imaging studies, radiologists can approximate your tumor’s size. While this may be straightforward in some cases, it may be more challenging in others. Not all tumors are simple, round shapes. For example, the tumor could be elongated like a baked potato and the image could be at an angle that makes it hard to see all of the dimensions. Some tumors even have irregular edges that make it hard to estimate the total diameter.
Size is divided into four classes in the TNM system:
|T-1||0 to 2 centimeters (cm)|
|T-2||2 to 5 cm|
|T-3||Greater than 5 cm|
|T-4||Tumor of any size that has broken through (ulcerated) the skin or is attached to the chest wall|
N=Lymph Node Status
Your surgeon may check your lymph nodes by palpating (feeling) the skin just above the lymph nodes and rating what they notice.
|N-0||The surgeon cannot feel any swollen nodes.|
|N-1||The surgeon can feel some swelling and thinks the nodes are positive (cancerous).|
|N-2||The lymph nodes feel like they are quite swollen, lumpy, and bunched together.|
|N-3||Swollen lymph nodes are near the collarbone.|
Alternatively, your lymph nodes may be evaluated via a sentinel node biopsy.
M = Metastasis
Metastasis, the extent to which the cancer has spread, also affects the stage of cancer.
|M-0||A sample of the nodes have been surgically removed and tested and are clear of cancer.|
|M-1||Nodes have cancer cells or micrometastases in them. The tumor has shed cells beyond its original location, and the cancer may be in other parts of the body.|
Putting It All Together
All of the TNM information will be combined twice, once by the surgeon and again by the pathologist. Each expert will give an opinion about your case in terms of its TNM stage. To officially determine the breast cancer stage, your team may need to know more about:
- The hormone receptor status
- The grade of the tumor (speed of growth)
- Where in your body the cancer has traveled to (if it has metastasized)
All of these factors affect your diagnosis and will be heavily considered when you and your healthcare provider look at treatment options.
Breast Cancer Treatment Options
The Stages of Breast Cancer
Breast cancer has four stages, and if pre-cancerous conditions are included, a fifth. Your stage depends on the tumor’s TNM rating.
Stage 0 (Precancer)
Stage 0 is used for precancerous, or in situ, carcinomas. In this stage, there’s no evidence that abnormal cells have broken out of the area where they originated or are invading neighboring tissues.
Stage 1 means it’s invasive cancer (cells are moving into surrounding tissues). There are two subcategories:
- The tumor measures up to 2 cm.
- Cancer cells have not spread out of the breast into the lymph nodes.
- A small group of cancer cells measuring between 0.2 millimeters (mm) and 2 mm is found in the lymph nodes.
- A stage 1A tumor may or may not exist.
Stage 2 is cancer that has become invasive. This stage also is divided into A and B subcategories.
- No tumor is in the breast, but cancer larger than 2 mm is present in lymph nodes, either axillary (under the arm) or near the breast bone.
- The tumor is smaller than 2 cm and has spread to the lymph nodes.
- The tumor measures between 2 and 5 cm and hasn’t spread to the lymph nodes.
Under certain conditions, tumors of this size may still be classified as stage 1.
- The tumor measures between 2 and 5 cm and small groups of cells (between 0.2 and 2 mm) exist in the axillary lymph nodes.
- The tumor measures 2 to 5 cm and there is cancer in up to three axillary lymph nodes.
- The tumor measures larger than 5 cm but isn’t in the axillary lymph nodes.
Stage 3 cancers are invasive. This stage is divided into three subcategories.
- Any size breast tumor (or no tumor) is present and cancer has been found in between four and nine lymph nodes.
- The tumor is larger than 5 cm and small groups of cancer cells (0.2 mm to 2 mm) are in the lymph nodes.
- The tumor is larger than 5 cm and cancer has spread to up to three lymph nodes.
Under certain conditions, tumors of this size may be classified as 1B.
- A tumor of any size has spread to the chest wall and/or skin and caused swelling or an ulcer.
- Cancer may have spread to up to nine axillary lymph nodes or may have spread to lymph nodes near the breast bone.
- The case fits the criteria for inflammatory breast cancer (skin on the breast is red and may feel warm or be swollen, and cancer has spread to the lymph nodes and possibly the skin).
Under certain circumstances, tumors meeting the first two criteria may be classified as stage 2A.
- A tumor of any size has spread to the chest wall and/or skin.
- Cancer has spread to 10 or more axillary lymph nodes.
- Cancer has spread to lymph nodes above or below the collarbone.
- Cancer has spread to lymph nodes near the breastbone.
Under certain circumstances, tumors meeting the above criteria may be classified as stage 3A.
Stage 4 is also called metastatic breast cancer. Rather than being confined to the breast and nearby lymph nodes, it’s traveled to other organs. Common metastases sites include the lungs, skin, bones, liver, brain, or distant lymph nodes.
It may also be a recurrence of breast cancer that has spread to other areas.
Tumor Size and Next Steps
Biopsies and imaging studies give an approximate measurement of your tumor, but you need the actual tumor size in order to make the best treatment decisions.
After a lumpectomy or mastectomy, your excised breast tissue will be combined with your biopsy tissue, and a pathologist will examine the true size of the mass. The pathological measurement of your tumor is the gold standard for tumor size. Your post-surgical pathology report will summarize your comprehensive diagnosis of breast cancer.
With that in mind, it may seem counterintuitive to rely on the tumor size estimations used in TNM staging. But there is good reason for this: Imaging allows you and your surgeon to make the most conservative choice when it comes to breast surgery. Your surgeon will use the information from previous tests as guidance when removing your tumor.
If a lumpectomy will remove your cancer, you may be able to avoid a mastectomy. If neoadjuvant chemo may shrink your tumor before surgery, then you may need less tissue removed in a lumpectomy. However, in some cases, such as widely scattered invasive breast cancer, a mastectomy might be the only surgical option.
Having the most information and understanding the implications of your tests helps you make informed, intelligent treatment decisions.
Breast Cancer Healthcare Provider Discussion Guide
Get our printable guide for your next healthcare provider’s appointment to help you ask the right questions.
A Word From Get Meds Info
When you plan a healthcare provider visit and you know that you will be discussing your diagnosis, lab results, or treatment plans, you may want to ask someone to come along with you to take notes. If that’s not possible, you may want to record the appointment on your phone or a small tape recorder, if permitted. News of any diagnosis often comes with a lot of information, medical terminology, and emotion. Having something you can refer back to can help if you leave your appointment and details are fuzzy.
American Joint Commitee on Cancer. Cancer Staging System.
American Cancer Society. Imaging Tests to Find Breast Cancer. Revised October 3, 2019.
American Cancer Society. Breast Cancer Stages. Revised September 20, 2019.
American Cancer Society. Cancer Staging. Revised March 25, 2015.
Cancer.net. Breast Cancer: Stages. Reviewed July 2019.
American Cancer Society. Understanding Your Pathology Report: Breast Cancer. Revised March 9, 2017.
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