What Do Those Breast Cancer Staging Letters and Numbers Mean?

Staging is the way doctors talk about how big a tumor is and how far it has spread. Staging helps doctors decide the best way to treat breast cancer. It also helps doctors estimate what a person’s outcome will be.

Staging for breast cancer is more complicated than for many other types of cancer. The information on this page gives you the basics. Talk with your doctor about any questions you may have.

How is the stage decided?

Doctors look at several things about your breast cancer to decide the stage. They look at1:

  • Size of the tumor
  • Whether it has spread to any lymph nodes
  • Whether it has spread far from the original location (called metastasis)
  • Test results that describe any potential biomarkers, or specific features of the cancer cells
  • How much the cancer cells look like healthy cells

Doctors get this information from a physical exam, imaging tests, blood tests, biopsies (tissue samples of the cancer and lymph nodes), and sometimes surgery.

More on this topic

All of this information goes into a sort of formula to find the best treatment for your specific needs. Things that may affect your treatments include:

  • Whether certain hormones or proteins are playing a role in the cancer
  • How advanced the cancer is
  • Whether you have gone through menopause
  • Your age and general health

AJCC staging system – the letters

In the United States, the American Joint Committee on Cancer (AJCC) system is used to stage breast cancers. The AJCC system combines letters and numbers to describe a person’s breast cancer. It begins with T, N, and M.1

  • T (tumor) = the size of the tumor and if it has spread to nearby areas
  • N (node) = if the cancer has spread to nearby lymph nodes and how many
  • M (metastasis) = if the cancer has spread to distant organs such as the bone, lungs, or liver. Cancer that has spread is called metastasized (meh-tas-ta-sized)

The letters TMN are followed by a number. The number describes the tumor’s size and how much it has spread. The higher the number, the bigger the tumor or the more it has spread. Depending on your cancer, you may also see other letters, such as1:

  • ER = the cancer has an estrogen receptor protein
  • PR = the cancer has a progesterone receptor protein
  • HER2 = the cancer makes too much HER2 protein
  • G = how much do the cancer cells looks like normal, healthy cells
  • X = tumor cannot be assessed
  • is = stands for carcinoma in situ. This means cancer cells are in the breast, say in a milk duct, but have not spread through the breast

AJCC staging system – the numbers

T, N, and M are followed by numbers. Higher numbers mean the cancer is larger or more widely spread.

The T (tumor size and spread) numbers mean1:

  • T0 = no evidence of tumor but some tests may say cancer cells are there
  • T1 = tumor is 2 centimeters across (¾ of an inch) or smaller across. An a, b, or c may be added after T1 to describe the tumor size more accurately.
  • T2 = tumor is more than 2 centimeters (¾ of an inch) but less than 5 centimeters (2 inches) across
  • T3 = tumor is more than 5 centimeters (2 inches) across
  • T4 = tumor can be any size that is growing into the chest wall or skin. Includes inflammatory breast cancer. An a, b, c, or d may be added after T4 to describe the tumor more accurately.

Breast cancer is considered advanced, or metastatic if it is stage 4.2

Figure 1. Overview of breast cancer stages

Four human figures, one per stage, each showing progression and presence of cancer as represented by that particular stage.

The N (lymph node) numbers mean1:

  • N0 = cancer has not spread to nearby lymph nodes. An i+ or mol+ may be added to describe cells in the lymph nodes more accurately.
  • N1 = cancer has spread to 1 to 3 underarm lymph nodes and/or cancer cells are found in small amounts in lymph nodes around the breastbone
  • N2 = cancer has spread to 4 to 9 lymph nodes under the arm or has caused some lymph nodes around the breastbone to get bigger
  • N3 = cancer has spread to lymph nodes under the arm, has spread to lymph nodes further from the breast, and/or has caused some lymph nodes to get bigger, along with 1 or more places where the cancer has spread and is larger than larger than 2 mm (smaller than ⅛ inch)

Any N may be followed with letters that describe the spread more accurately. The letters you may see include: a, b, c, i+, mi, mol+.1

The M (metastasis) numbers mean1:

  • M0 = cancer does not seem to have spread to bone or organs further from the breast
  • M1 = cancer has spread to what are called distant organs. The most common areas of spread are the bones, lungs, brain, or liver.

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Jessica Johns Pool | Last reviewed: February 2021