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The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on March 22, 2021.

Breast cancer stages

You learned the stage of your breast cancer, but do you understand what it means?

Cancer stages involve myriad measurements and factors, making the process tricky to unravel—but vital.

Understanding your stage will help you and your care team make informed treatment decisions, including whether a clinical trial might be best suited for you.

Medical advances have broadened our knowledge about breast cancer and how to stage it, and those revelations have yielded improved treatments, too.

Below, you can learn more about breast cancer staging and the terms your care team may use.

Stages of breast cancer

Your breast cancer stage indicates the severity of the disease upon diagnosis. Your cancer will always retain that label, regardless of its progress.

Breast cancer staging is classified by:

  • The size and location of the tumor
  • Whether the cancer has spread to nearby lymph nodes or other parts of the body
  • The grade of the tumor—or how likely it is to grow and spread
  • Whether certain biomarkers—hormone receptors or other proteins—have been found

All these attributes help your care team determine how to treat your cancer.

To assess the location, size and spread of cancer, your care team will use the TNM Staging System, developed and updated for breast cancer by the American Joint Committee on Cancer (AJCC).

  • TNM stands for Tumor-Node-Metastasis, which are important factors in determining the severity of your cancer.
  • All cancers may be evaluated by TNM markers, but breast cancer staging also uses a few extra criteria for a more detailed description.
  • Ultimately, your specific combination of TNM and these other markers will determine your cancer’s stage.

Breast cancer has five general stages under the TNM system: 0 through IV.

What is stage 0 breast cancer?

Stage 0, known as carcinoma in situ, means cancer cells are present but have been caught so early that they haven’t spread. In the ducts, it’s called ductal carcinoma in situ (DCIS) and referred to as noninvasive.

What is stage I breast cancer?

Stage I means the tumor is very small and either has not spread or may have a tiny bit of spread in a nearby lymph node. A cancer that has spread into the surrounding area is referred to as invasive breast cancer.

  • Stage IA: The tumor is very small and has not spread to the lymph nodes.
  • Stage IB: Cancer between 0.2 mm and 2 mm is found in the lymph nodes (the breast tumor can’t be detected or is smaller than 20 mm).

What is stage II breast cancer?

Stage II means the tumor is larger than at stage I and may have spread to a few nearby lymph nodes.

  • Stage IIA: Though it can’t be detected, the tumor has spread to one to three  lymph nodes (but has not spread to other parts of the body), or the tumor is 20 mm or smaller and has spread to one to three lymph nodes, or the tumor is 20 mm to 50 mm and has not spread to lymph nodes.
  • Stage IIB: The tumor is 20 mm to 50 mm and has spread to one to three lymph nodes, or the tumor is larger than 50 mm but has not spread to any lymph nodes.

What is stage III breast cancer?

Stage III means the tumor is larger than at stage II and/or has spread to several lymph nodes and/or tissue around the breast or breast bone.

  • Stage IIIA: The tumor has spread to four to nine lymph nodes or to mammary lymph nodes, but not to other parts of the body; or the tumor is larger than 50 mm and spread to one to three lymph nodes.
  • Stage IIIB: The tumor has spread to the chest area or caused the breast to swell, or it is inflammatory breast cancer. It may have spread to up to nine lymph nodes but has not spread to other parts of the body.
  • Stage IIIC: This refers to any tumor that has spread to 10 or more lymph nodes, including those under the collarbone, but has not spread to other parts of the body.

What is stage IV breast cancer?

Stage IV means the cancer has metastasized, or become mobile, and spread to distant parts of the body, typically the bones, lungs or liver. This is an advanced stage of cancer, called metastatic breast cancer.

Your cancer will be clinical staged based on diagnostic tests, a pathological staged after surgery (which allows your care team to closely study the cancerous tissue).

The TNM system explained

TNM staging involves quite a bit of detailed information. Let’s break down this system:

T refers to the size of the tumor.

An imaging technique may be used to measure the tumor. The designations are:

  • Tx: Tumor cannot be evaluated.
  • T0: There’s no evidence of a tumor.
  • Tis: This is carcinoma in situ, which means cancerous cells were caught before tumor growth.
  • T1: Tumor is smaller than 2 cm across.
  • T2: Tumor is 2 to 5 cm across.
  • T3: Tumor is larger than 5 cm across.
  • T4: Any size tumor is growing into chest walls or skin

N refers to spread to nearby lymph nodes.

Lymph nodes are pockets in your lymphatic system, which is similar to the circulatory system. Instead of blood, it transports a fluid called lymph. White blood cells are key immune cells that cluster in your lymph nodes, waiting to defend against foreign invaders. Cancer can spread to these nodes.

The cancer found in lymph nodes may be small (micrometastasis: 0.2 mm to 2 mm) or large (macrometastasis: bigger than 2 mm). The designations are:

  • Nx: Lymph nodes cannot be evaluated.
  • N0: There’s no evidence of spread.
  • N1: Cancer has spread to a few axillary (underarm) lymph nodes or in smaller amounts to nodes near the breastbone.
  • N2: Cancer has spread to more axillary lymph nodes than under N1 or made breastbone lymph nodes look bigger.
  • N3: Cancer has spread significantly to axillary lymph nodes or may be near or above the clavicle (collarbone). Alternatively, fewer axillary lymph nodes are involved, but there are areas of macrometastasis (greater than 2 mm) and enlargement.

M refers to the spread to more distant parts of the body, or metastasis.

  • Mx: Metastasis cannot be evaluated.
  • M0: There’s no evidence of spread.
  • M1: The cancer has spread to distant organs or tissues.

Additional markers for breast cancer staging

Additional markers specific to breast cancer will further define your stage, which may be helpful in choosing targeted treatments to fight the cancer.

  • ER: The cancer has an estrogen receptor. Estrogen is a hormone, and some cancers have receptors that respond to estrogen.
  • PR: The cancer has a progesterone receptor. Progesterone is also a hormone.
  • HER2: The cancer makes the protein HER2 (human epidermal growth factor).
  • G: Grade of cancer refers to how different the cells look from normal. Grade 1 indicates that the cells look fairly normal, while grade 2 cells are growing a little faster, and grade 3 cells look markedly different than normal breast tissue.

These markers, along with the TNM measurements, define your stage.

A cancer recurrence refers to cancer that returns in the same breast, and it requires new staging. This new stage is marked by an “R” at the end to indicate “restaging.” If it develops in the other breast, it’s considered a new cancer.

Putting it together

Your breast cancer stage is specific to you. It’s based on all the factors collected through diagnostic tests and/or surgery, and it helps your care team assess your prognosis.

The American Cancer Society offers examples of how to interpret a breast cancer stage. For example, a cancer that’s T2, grade 3, no spread to lymph nodes (N0) or body (M0), HER2-negative and ER- and PR-positive is stage IB.

Diagnostic tests that inform the clinical stage

Many methods are used to detect and stage cancer. Some of the common tests include:

Biopsy: The doctor uses a needle to extract breast tissue or fluid, which is then sent to a lab. There, various techniques are used to examine different attributes, such as hormone receptor or HER2 status. (Sometimes the tissue sample is collected during a surgical procedure informing the pathological stage.)

Tumor markers: Rapidly dividing cancerous cells interrupt some of the normal mechanisms of cell growth. This causes the cell to overproduce certain molecules. Lab tests detect these compounds, known as tumor markers, in blood or tissue samples.

Imaging techniques: Several different scans are used to examine characteristics of your cancer. Below are some of the noninvasive imaging techniques you might encounter:

  • The size and location of the tumor
  • Whether the cancer has spread to nearby lymph nodes or other parts of the body
  • MRI (magnetic resonance imaging) scans use magnets and radio waves to generate detailed pictures of your tissues.
  • CT (computed tomography) scans use X-rays to look at your organs.
  • Nuclear scans trace the flow of an injected safe radioactive dye in your body.
  • PET (positron emission tomography) scans are similar to nuclear scans but specifically examine glucose consumption in the body—since cancer cells use more glucose than normal cells.
  • Ultrasound imaging uses sound waves to see inside your body

Why is staging important?

During your initial diagnosis, you and your cancer team will work together to develop a treatment plan. Staging allows you to answer the following questions:

  • How does this cancer typically progress?
  • Which treatments may work?

Some of the staging may be even more in-depth, but in general, it’s designed to prepare a more tailored approach to your disease. Your care team will be able to explain any new terms and what they mean for you.