After a breast cancer diagnosis, doctors give the cancer a stage from 0 to 4. The stage number describes whether the cancer has spread, and if so, where in the body it has spread.

Cancer stages are broken down further into subcategories to provide more specific information. For example, the stage will include:

• The size of the tumor

• Whether the cancer is in lymph nodes, and if so, how many lymph nodes are involved

• Whether the cancer has receptors for the hormones estrogen, progesterone, or both, and if it makes too much of a protein called human epidermal growth factor receptor 2 (HER2)

This information helps your doctor choose the right treatment for you. It can also give you an idea of what outlook to expect.

Doctors stage breast cancer in two ways:

• Clinical staging is based on the results of a physical exam, imaging tests like mammogram and magnetic resonance imaging (MRI), and biopsy results.

• Pathologic staging is done with tissue removed during surgery. It’s based on the tumor size, features of the cancer, and lymph nodes involved.

The cancer stage starts with a number from 0 to 4. The higher the number, the farther the cancer has spread.

To determine this number, doctors use a system of factors, including the TNM system. This includes:

• T (Tumor Size) This is measured on a scale from 0 to 4. The higher the number, the larger the tumor is and the more it has spread into tissues near the breast.

• N (Node) This is measured from 0 to 3. The higher the number, the more lymph nodes near the breast contain cancer. Once cancer is in the lymph nodes it can spread to other parts of the body.

• M (Metastasis) This indicates whether the cancer has spread to distant organs like the bones, liver, brain, or lungs. M is followed by the number 0 or 1, where 0 means the cancer hasn’t spread and 1 means the cancer has reached other parts of the body.

Breast cancer stages also consider these characteristics of the cancer:

• Grade This is measured from 1 to 4 and describes how much the cancer cells look like healthy cells. High-grade cancers look more abnormal and tend to grow more quickly than low-grade ones.

• Estrogen Receptor (ER) Status This checks whether the cancer cells grow in response to the hormone estrogen. If they do, it’s ER-positive. If not, it’s ER-negative.

• Progesterone Receptor (PR) Status This checks if the cancer cells grow in response to the hormone progesterone. If they do, it’s PR-positive. If not, it’s PR-negative.

• HER2 Status Do the cancer cells have too much of the HER2 protein, which makes them more aggressive? If so, it’s HER2-positive. If not, it’s HER2-negative.

Pathological staging can also include the Oncotype DX score. This genetic test is used for certain hormone receptor–positive tumors. It helps predict the likelihood of the cancer coming back (recurring) after treatment. A low score (0 to 25) means a low risk of recurrence, while a high score (26 to 100) means a high risk of recurrence.

Stage 0

Stage 0 breast cancer is only in the ducts — the tubes that carry milk to the nipple during breastfeeding. It hasn’t spread to surrounding tissues. Another name for cancer that hasn’t spread beyond the milk ducts is noninvasive breast cancer. Ductal carcinoma in situ (DCIS) is a type of noninvasive breast cancer.

Stage 1

Stage 1 cancer is invasive. Cancer cells have spread to nearby breast tissue. Doctors further divide stage 1 breast cancers into two types:

• Stage 1A The cancer is 2 centimeters (cm) across or smaller and it has not spread into the lymph nodes or outside of the breast.

• Stage 1B Small clumps of cancer cells up to 2 millimeters (mm) in size are in the lymph nodes. There may not be a tumor in the breast, but if there is, it’s no bigger than 2 cm.

Stage 2

At this stage the cancer is larger and it may have spread to axillary lymph nodes or lymph nodes near the breastbone.

• Stage 2A There may be no tumor in the breast, or there is a tumor in the breast measuring 2 cm or less, and cancer has spread to up to three lymph nodes. Or, there’s a 2 to 5 cm tumor in the breast with no spread to lymph nodes.

• Stage 2B The tumor measures 2 to 5 cm and cancer has spread to up to three axillary lymph nodes or to lymph nodes near the breastbone. Or the tumor is bigger than 5 cm and it hasn’t spread to the axillary lymph nodes.

Stage 3

By stage 3 the cancer is typically larger and it may have spread to more lymph nodes. This stage is divided into three substages:

• Stage 3A The tumor can be any size, and the cancer has spread to four to nine axillary lymph nodes. Or the tumor is larger than 5 cm and the cancer has spread to up to three axillary lymph nodes.

• Stage 3B The tumor can be any size and cancer has reached the chest wall or skin. The cancer may have spread to up to nine axillary lymph nodes or to lymph nodes.

• Stage 3C The cancer may be any size and has spread to 10 or more axillary lymph nodes.

Breast cancer that hasn’t spread beyond the axillary lymph nodes (stages 0 through 2, and sometimes 3A) is also called early breast cancer.Inflammatory breast cancer is always at least stage 3B. Symptoms of inflammatory breast cancer include breast redness, swelling, and warmth. Cancer cells have spread to the lymph nodes and may also be in the skin of the breast.

Stage 4

Also called metastatic breast cancer or advanced breast cancer, stage 4 breast cancer has spread beyond the breast and lymph nodes to other parts of the body. The bones, lungs, brain, and liver are common sites of breast cancer spread.Breast cancer is treatable but usually not curable at stage 4. At this stage, the cancer is M1 since it has spread to distant organs.

In addition to physical exams, doctors use imaging tests, biomarker tests, and biopsy results to stage breast cancer.

Imaging Tests

These tests find cancer in the breast and in other parts of the body.

Mammogram The same test you get for breast cancer screening is also part of the diagnosis. A mammogram uses X-rays to take pictures of the inside of the breast. Doctors use mammography to determine how large the cancer is and where in the breast it’s located. This test can also show whether cancer is in lymph nodes near the breast.

Ultrasound This test uses sound waves to see inside your breasts. Your doctor can use ultrasound to confirm the diagnosis and find out where the cancer is in your breast.

Magnetic Resonance Imaging (MRI) An MRI uses powerful magnets and radio waves to create images of your breasts. This test can locate the cancer in the breast and measure the tumor size. It may also help detect some cancers before they’re seen on a mammogram or ultrasound.

Computerized Tomography (CT) Scan This test takes many X-ray pictures of the breasts from different angles and combines them into a very detailed cross-sectional image. A CT scan is usually used for staging purposes, after a patient has already received a breast cancer diagnosis. For example, it can show whether the cancer has spread into the chest wall.

Positron Emission Tomography (PET) Scan A PET scan uses a radioactive tracer to find areas of cancer throughout the body.

Chest X-Ray This test can show whether the cancer has spread to the lungs.

Bone Scan This test can find breast cancer that has spread to the bones. A radioactive material injected into a vein collects in areas of the bone that contain cancer.

Breast Biopsies

A biopsy removes a sample of tissue from the tumor, or takes out suspicious lymph nodes to test them for cancer. Many biopsy methods are minimally invasive, but surgical biopsy under sedation may sometimes be necessary. Surgical biopsy is usually done during the definitive breast surgery, like a lumpectomy or mastectomy.

Biomarker Tests

If imaging and biopsy testing detects cancer, biomarker tests help your doctor determine the specific characteristics of your breast cancer to find the right treatment for it. These tests are done on a sample of the tumor taken during a biopsy or breast surgery.

Hormone Receptor Status Does the cancer have receptors for the hormones estrogen, progesterone, or both?

HER2 Status: Does the cancer make too much of the HER2 protein?

Tests for these biomarkers may sometimes be done to find the right treatment:

• Proteins like PD-L1 and Ki-67 that can affect the growth of cancer cells

• Gene mutations like BRCA1 and BRCA2 and PIK3CA

The breast cancer stage is one factor that goes into determining your prognosis. The lower the stage, the less the cancer has spread and, generally, the better the outlook.

The five-year relative survival rate compares the likelihood that someone with breast cancer will survive for at least five years after their diagnosis with the outlook of people in the general population. The American Cancer Society’s five-year relative survival rates for breast cancer are:

• Localized (no cancer outside the breast): 99 percent

• Regional (the cancer has spread to nearby structures or to lymph nodes): 87 percent

• Distant (the cancer has spread to organs like the bones, liver, or lungs): 33 percent

These numbers don’t tell the whole story, though. Other factors also go into the prognosis, including:

• Cancer subtype (hormone receptor–positive, HER2-positive, etc.)

• Grade, or how different the cancer cells look from healthy cells

• Whether cancer has spread to the lymph nodes, and if so, how many lymph nodes are involved

Your prognosis could also change. For example, it’s possible to be diagnosed with an early-stage breast cancer, only to have the cancer return at a higher stage or spread after treatment. Also, each person with breast cancer is different. Statistics can’t predict exactly how your cancer will progress or respond to treatment.

• Understanding the stage of breast cancer indicates how far the cancer has spread, which is essential for determining the most effective treatment options.

• Biomarker tests, including estrogen and progesterone receptor status and HER2 status, are important to tailor treatment and potentially improve outcomes for individuals with breast cancer.

• For anyone diagnosed with breast cancer, particularly in more advanced stages, it’s vital to talk with healthcare professionals about all treatment possibilities to manage the disease progression effectively and improve quality of life.

• If you experience new symptoms or notice significant changes in your health, seek medical attention promptly for proper evaluation, as swift action can impact prognosis positively.