Breast cancer develops in the tissues of the breast and is classified into five stages—stage 0 through stage 4—based on how far the cancer has progressed. These stages guide your treatment plan and give insight into your prognosis.
How is breast cancer stage determined?
After a diagnosis, your doctor will use several diagnostic tools and procedures to determine the stage of breast cancer. These may include physical examinations, imaging tests such as mammograms, CT or MRI scans, and ultrasounds, as well as blood tests and biopsies. Biopsies help assess hormone receptor status and HER2 protein presence.
The most widely used classification system is the TNM staging system developed by the American Joint Committee on Cancer (AJCC). It assesses:
- T (Tumor): The size and location of the original tumor.
- N (Nodes): Whether the cancer has spread to nearby lymph nodes and to what extent.
- M (Metastasis): Whether the cancer has spread to distant parts of the body.
Additional factors include tumor grade, hormone receptor status, and HER2 status.
Breast cancer stages
Here’s a clear and structured summary of what each stage of breast cancer means:
Stage 0
This is known as noninvasive breast cancer. The tumor is only present within the breast lobules (glands that can make milk) and ducts (tubes that can carry breast milk to the nipple).
Stage 1
The cancer is now invasive, may measure up to 2 centimeters (cm), and may be found in the lymph node.
Stage 2
This describes when breast cancer is up to 2–5 cm (or larger) or has spread to one to three lymph nodes.
Stage 3
The cancer has spread to four to nine lymph nodes, or the tumor is larger than 5 cm and has spread to one to three lymph nodes, or the tumor is any size but has spread to the chest wall.
Stage 4
This is the most advanced stage of breast cancer. The cancer has spread beyond the breast and nearby tissues to distant organs like the liver, bone, and brain.
Preventing or slowing cancer progression
While you cannot always prevent breast cancer, maintaining a healthy lifestyle can reduce your risk or help slow progression. This includes staying active, eating a balanced diet, maintaining a healthy weight, avoiding alcohol, quitting smoking, and asking your doctor about supplements like vitamin D.
What is restaging?
If breast cancer returns or progresses after treatment, your doctor may "restage" it to re-evaluate the extent of the disease. This involves updated imaging, tests, or biopsies and helps guide the next course of treatment.