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If you have breast cancer, your doctor will need to know how serious it is. To do this, your doctor will figure out the stage of your cancer and possibly the grade of your cancer. Knowing your stage and grade will help your doctor decide which treatments are best for you.

When your breast cancer is staged, it is classified according to three things.

• How big your breast cancer (tumor) is, and whether it has spread from the breast tissue into the nearby skin and muscles.
• Whether your breast cancer has spread to your lymph nodes (these small collections of cells are part of your immune system).
• Whether your breast cancer has spread to other parts of your body.

These three things are used together and called the TNM classification:¹

• T is for tumor
• N is for (lymph) nodes
• M is for metastasis. (Metastasis is when the cancer spreads to other parts of your body, such as your liver or lungs.)

Each factor is given a number.

• For T, the number tells you how big the tumor is.
• For N, the number shows which lymph nodes have cancer cells in them.
• For M, the number tells you whether your breast cancer has spread outside your breast and the nearest lymph nodes to other parts of your body.

Generally, lower numbers mean your cancer is less serious. For example, if your cancer was classified as T1N0M0, this would show that you had a small tumor that had not spread to the lymph nodes nearest to it or to other parts of your body.

Here's what the different classifications mean.

T (tumor)

• Tis: This is also called cancer in situ or carcinoma in situ. It means your breast cancer hasn't spread beyond the lining of the ducts.
• T1: Your breast cancer is 2 centimeters (around three-quarters of an inch) or less across.
• T2: Your breast cancer is more than 2 centimeters (around three-quarters of an inch) but no bigger than 5 centimeters (around 2 inches) across.
• T3: Your breast cancer is bigger than 5 centimeters (around 2 inches) across.
• T4: Your tumor extends from the breast into your chest wall or your skin. Or the tumor is inflammatory. (Inflammatory cancer is a rare, invasive cancer that can block the lymph vessels in the skin over the breast.)

N (lymph nodes)

• N0: Your breast cancer has not spread to the nearest lymph nodes (local lymph nodes).
• N1: Your breast cancer has spread to the lymph nodes on the same side of your body as your breast cancer, and these can be moved around (they are not joined together by the cancer).
• N2: Your breast cancer has spread to lymph nodes that can't be moved (they are joined together by the cancer) on the same side of your body as your breast cancer.
• N3: Your breast cancer has spread to lymph nodes toward the middle of your body (the internal mammary nodes) on the same side as your breast cancer.

M (metastasis)

• M0: Your breast cancer has not spread to another part of your body.
• M1: Your breast cancer has spread to a distant part of your body. This is called metastasis. This may mean it has spread to lymph nodes above the collarbone on the same side of your body as your breast cancer, or to your bones, liver or lungs.

Once your doctor has your TNM classification, he or she uses it to figure out your cancer stage. Doctors divide cancer into four main stages. Most doctors use the American Joint Committee on Cancer staging system.²

Stage 1

Stage 1 breast cancer means:

• The tumor (lump or patch of cancer cells) is no more than 2 centimeters (around three-quarters of an inch) across
• The lymph nodes in the armpit aren't affected
• The cancer hasn't spread to another part of the body
• This is often called early breast cancer.

Stage 2

Stage 2 breast cancer means that the tumor is bigger than 2 centimeters (around three-quarters of an inch) but smaller than 5 centimeters (around 2 inches), or the lymph nodes in the armpit are affected. It also means that the cancer hasn't spread to another part of the body.

• When the tumor is 2 centimeters (around three-quarters of an inch), this is often called early breast cancer.
• When the tumor is closer to 5 centimeters (around 2 inches), this is often called locally advanced breast cancer.

Stage 3

Stage 3 breast cancer means:

• The tumor is bigger than 5 centimeters (around 2 inches) across
• The cancer is in the nodes in the armpit
• The cancer hasn't spread to another part of the body
• This is often called locally advanced breast cancer.

Stage 4

Stage 4 breast cancer means:

• The tumor can be any size
• The cancer is in the nodes in the armpit
• The cancer has spread to other parts of the body
• This is often called metastatic or secondary breast cancer.

Doctors also divide some of these stages further. For example, stage 2 is divided into 2A and 2B. To read more about how doctors stage cancer using the TNM system and American Joint Committee on Cancer staging system, see Cancer staging table.

Your doctor may also tell you about the grade of your cancer. The grade describes how much the cancer cells look like normal breast cells when viewed under a microscope.

Doctors usually grade cancer as low grade or high grade. Low-grade cancer cells look similar to normal cells. High-grade cancer cells look very different from normal breast cells.

The more the cells look like normal cells, the better your outlook may be. You may also hear your cancer grade described as a number between 1 and 4. A lower number means a lower grade.

You and your doctor can use information about the size of your breast cancer, whether it has spread to your lymph nodes, and what it looks like under a microscope to discuss the best treatment for you.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.