When breast cancer is first diagnosed, it’s also assigned a stage. The stage refers to the size of the tumor and where it has spread.

Doctors use a variety of tests to find out the stage of breast cancer. These can include imaging tests, like a CT scan, MRI, ultrasound, and X-ray, as well as blood work and a biopsy of the affected breast tissue.

In order to get a better understanding of your diagnosis and treatment options, you’ll want to know what stage the cancer is in. Breast cancer that’s caught during the earlier stages is likely to have a better outlook than cancer caught during later stages.

The staging process determines whether cancer has spread from the breast to other parts of the body, like the lymph nodes or major organs. The most commonly used system is the American Joint Committee on Cancer TNM system.

In the TNM staging system, cancers are classified based on their T, N, and M stages:

  • T indicates the size of the tumor and how far it has spread within the breast and to nearby areas.
  • N stands for how much it has spread to lymph nodes.
  • M defines metastasis, or how much it has spread to distant organs.

In TNM staging, each letter is associated with a number to explain how far the cancer has progressed. Once the TNM staging has been determined, this information is combined into a process called “stage grouping.”

Stage grouping is the common staging method in which stages range from 0 to 4. The lower the number, the earlier the cancer stage.

This stage describes noninvasive (“in situ”) breast cancer. Ductal carcinoma in situ (DCIS) is an example of stage 0 cancer. In DCIS, the precancerous cells may have just started to form but haven’t spread beyond the milk ducts.

This stage marks the first identification of invasive breast cancer. At this point, the tumor measures no more than 2 centimeters in diameter (or about 3/4 inch). These breast cancers are subdivided into two categories (1A and 1B) based on a number of criteria.

Stage 1A means that the tumor is 2 centimeters or smaller, and that the cancer hasn’t spread anywhere outside the breast.

Stage 1B means that small clusters of breast cancer cells are found in the lymph nodes. Typically at this stage, either no discrete tumor is found in the breast or the tumor is 2 centimeters or smaller.

This stage describes invasive breast cancers in which one of the following is true:

  • The tumor measures less than 2 centimeters (3/4 inch), but has spread to lymph nodes under the arm.
  • The tumor is between 2 and 5 centimeters (about 3/4 inch to 2 inches) and may or may not have spread to lymph nodes under the arm.
  • The tumor is larger than 5 centimeters (2 inches), but hasn’t spread to any lymph nodes.
  • No discrete tumor is found in the breast, but breast cancer larger than 2 millimeters is found in 1–3 lymph nodes under the arm or near the breastbone.

Stage 2 breast cancer is divided into stage 2A and 2B.

In stage 2A, no tumor is found in the breast or the tumor is smaller than 2 centimeters. Cancer may be found in the lymph nodes at this point, or the tumor is larger than 2 centimeters but smaller than 5 centimeters and the cancer has not spread to the lymph nodes.

In stage 2B, the tumor may be larger than 2 centimeters but smaller than 5 centimeters, and breast cancer cells are found in the lymph nodes, or the tumor may also be larger than 5 centimeters, but cancer hasn’t spread to the lymph nodes.

Stage 3 cancers have moved to more breast tissue and surrounding areas but have not spread to distant areas of the body.

  • Stage 3A tumors are either larger than 5 centimeters (2 inches) and have spread to one to three lymph nodes under the arm, or are any size and have spread into multiple lymph nodes.
  • A stage 3B tumor of any size has spread to tissues near the breast — the skin and chest muscles — and may have spread to lymph nodes within the breast or under the arm.
  • Stage 3C cancer is a tumor of any size that has spread:
    • to 10 or more lymph nodes under the arm
    • to lymph nodes above or beneath the collarbone and near the neck on the same side of the body as the affected breast
    • to lymph nodes within the breast itself and under the arm

Stage 4 breast cancer has spread to distant parts of the body, such as the lungs, liver, bones, or brain. At this stage, cancer is considered advanced and treatment options are very limited.

The cancer is no longer curable because major organs are being affected. But there are still treatments that can help improve and maintain a good quality of life.

Because cancer may not have noticeable symptoms during the early stages, it’s important to get regular screenings and tell your doctor if something doesn’t feel normal. The earlier breast cancer is caught, the better your chances are of having a positive outcome.

Learning about a cancer diagnosis can feel overwhelming and even scary. Connecting with others who know what you’re experiencing can help ease these anxieties. Find support from others who are living with breast cancer.

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