The stage of a cancer, sometimes referred to as TNM (tumor, node, metastasis), is used to determine the type of treatment a patient should receive. It is calculated based on several factors:
- the size of the tumor (T)
- whether or not the cancer has spread to the axillary (armpit) lymph nodes, and if so, to how many (N)
- if the cancer has spread to other lymph nodes of the neck or chest area, or to other parts of the body (M)
Tests that may be used to determine how far a breast cancer has spread include a chest x-ray and blood tests. In some cases, a physician might also order a bone scan, a CT scan, a PET scan, or an MRI scan to assess the extent of the disease.
Breast cancer is also staged by number, based on the size of the tumor and how far it has spread.
Stage 0 is also called ductal carcinoma in situ (DCIS). In DCIS, cancer cells are still within a duct and have not invaded deeper into the surrounding fatty breast tissue. Paget disease (a cancer of the nipple that is very rare in men) is also stage 0 if there is no underlying tumor mass.
Stage I describes a tumor that is 2 cm or less and has not spread to the lymph nodes, or — if it has spread there — the cancer in the lymph nodes is microscopic (less than 2 mm in size).
Stage II describes a tumor that is between 2 and 5 cm or has spread to a few lymph nodes in the armpit.
Stage III describes a tumor that has spread to a greater number of lymph nodes in the armpit or has spread to other lymph nodes, such as those above the collarbone. It may have also grown into the chest wall.
Stage IV cancer can be any size and may or may not have spread to nearby lymph nodes. It has spread to distant organs (the most common sites are the bones, liver, brain, or lungs) or to lymph nodes far from the breast.
Tumor grade is an evaluation of how abnormal or disorganized the cells from a tumor appear when examined under a microscope. In general, a lower grade implies a less aggressive tumor.
Lymphovascular or Perineural Invasion
Sometimes tumor cells can invade the blood vessels or the lymph or nerve channels within breast tissue.