By Mayo Clinic Staff

Many people diagnosed with breast cancer are interested in knowing the stage of their cancer. A breast cancer stage is a way of saying how large a cancer is and whether it has spread. The stage also is one piece of information the healthcare team uses to understand the chances that treatment will be successful.

Your breast cancer stage can't tell your future, but it might help you understand more about your outlook. If you're interested in knowing your stage, here's some basic information about breast cancer staging to help you get ready to talk about it with your healthcare team.

Breast cancer stages range from 0 to 4. A lower number typically means the cancer is smaller and might only be in the breast. As the cancer grows larger or spreads beyond the breast, the numbers get higher.

Sometimes you might see the stages written using Roman numerals. The stages of breast cancer in Roman numerals are 0, I, II, III and IV.

There are different kinds of breast cancer staging. They may use different pieces of information to find the stage. Information that can be used in breast cancer staging includes:

• The size of the cancer in the breast. Healthcare professionals use millimeters to measure cancers. A smaller breast cancer generally has a better prognosis.
• Whether cancer cells have spread to the lymph nodes. Lymph nodes are part of the body's germ-fighting immune system. When breast cancer spreads, it often goes to the nearby lymph nodes first. The lymph nodes most often affected by breast cancer are the ones in the breast tissue and in the armpit. Breast cancer that hasn't spread to the lymph nodes generally has a better prognosis.
• Whether cancer cells have spread to other parts of the body. Breast cancer cells that break away from where they started can enter the blood vessels or the lymphatic vessels. The cells can use those vessels to travel to other parts of the body. Breast cancer that spreads to other parts of the body generally has a poorer prognosis.
• The cancer's grade. The grade tells the healthcare team how quickly the cancer is growing. Grades range from 1 to 3. A grade 1 cancer is growing slowly. A grade 3 cancer is growing quickly. A slow-growing cancer generally has a better prognosis.
• Hormone receptor status. Most breast cancer cells use the hormones estrogen and progesterone to help them grow. If you have a hormone receptor positive cancer, it means that the cancer cells have hormone receptors. The receptors catch the hormones circulating in the body. Medicine to block the hormones in the body works on these cancers. Breast cancers that have hormone receptors generally have a better prognosis.
• HER2 status. Some cancers make too much of a protein called HER2. These are called HER2-positive cancers. Medicine that targets cells making the HER2 protein works on these cancers. HER2-positive breast cancers generally have a better prognosis.
• Gene expression test results. Gene expression tests look for certain genes inside the cancer cells. The results can give the healthcare team a better idea of whether the cancer is likely or not likely to come back after treatment. One gene expression test is used in breast cancer staging, but it's only used in some situations. Not everyone needs this test.

Different kinds of breast cancer staging exist. Each kind of staging uses the numbers 0 to 4. What's different about the kinds of staging is:

• The kind of information that's used to decide on the stage.
• What the stage means and what it tells the healthcare team about the cancer.

Here's a look at the different kinds of breast cancer staging.

Anatomic breast cancer staging tells the healthcare team about the extent of the cancer. It uses only basic information about the cancer, including:

• The size of the cancer in the breast.
• Whether cancer is detected in the lymph nodes and which lymph nodes are affected.
• Whether there are signs that the cancer has spread to other parts of the body.

In this kind of staging, a lower number typically means the cancer is small or only in the breast. When the cancer moves to the lymph nodes or grows larger, the stages get higher.

Prognostic breast cancer staging uses much more information than does anatomic staging. Healthcare professionals in the United States started using this kind of staging in 2018.

To decide on the prognostic stage, the healthcare team uses:

• The size of the cancer in the breast.
• Whether cancer is detected in the lymph nodes and which lymph nodes are affected.
• Whether there are signs that the cancer has spread to other parts of the body.
• Cancer grade.
• Hormone receptor status.
• HER2 status.
• Gene expression test results, used when prognostic staging takes place after surgery.

Prognostic staging can be done at different times for different reasons:

• Clinical prognostic staging is done before treatment starts. The healthcare team uses results from imaging tests, biopsies and physical exams to decide on the stage. For those who are receiving medicine as the first treatment and those who won't have surgery, this kind of staging is thought to be most accurate.
• Pathological prognostic staging is done after surgery. Tissue removed during surgery goes to a lab for analysis. Doctors in the lab, called pathologists, measure the cancer and test lymph nodes for cancer. The healthcare team uses those results to decide on the stage. For those having surgery for breast cancer as their first treatment, this kind of staging is thought to be most accurate.

In prognostic staging, a lower number generally means the cancer is more likely to be cured and not come back. A higher number means the cancer is more likely to return after treatment.

In prognostic breast cancer staging, it's hard to summarize what each stage means. There are many factors that go into deciding on the stage. Two people with the same size cancer could have different stages.

Here's a general idea of what the breast cancer stages mean:

Stage 0 breast cancer. A stage 0 breast cancer is sometimes called a noninvasive breast cancer. This means that the cancer cells are inside a duct in the breast. The cells haven't broken out into the breast tissue. Stage 0 breast cancer also is called ductal carcinoma in situ. A breast cancer diagnosed at stage 0 has an excellent prognosis. It is very likely to be cured.

Stage 1 breast cancer. A stage 1 breast cancer is an invasive cancer. That means the cancer cells have grown into the breast tissue. A stage 1 breast cancer generally is a small cancer. Some stage 1 breast cancers have spread to nearby lymph nodes. A stage 1 cancer has a very good prognosis. Most people can be cured.

Stage 2 breast cancer. A stage 2 breast cancer is an invasive cancer. It may be larger than a stage 1 breast cancer or it might involve more lymph nodes. Stage 2 breast cancer has a higher risk of coming back after treatment than does a stage 1 breast cancer.

Stage 3 breast cancer. A stage 3 breast cancer is often more difficult to treat than a stage 1 or stage 2 breast cancer. Stage 3 breast cancers have either grown quite large or spread to many lymph nodes. Or both may be true. There is a higher risk that a stage 3 cancer will come back after treatment.

Stage 4 breast cancer. A stage 4 breast cancer is any breast cancer that spreads to other parts of the body. Breast cancer most often spreads to the bones, brain, lungs and liver. Treatments may help control the cancer, but often a cure isn't possible.

This is a good question for your healthcare professional. While stages give information about prognosis in general, they can't state your outlook exactly.

The stages are based on research that uses data from thousands of people with breast cancer. The stage may give a general idea of the outlook for people in your situation.

There are many things that might affect your personal outlook. These might include your overall health, age and other health conditions. Ask your healthcare team about your breast cancer stage and what it means for you. Your care team can help explain any personal factors that might affect your prognosis.