Once breast cancer has been diagnosed, doctors perform tests to determine the stage of the cancer. Staging is the process of determining the size of the tumor and whether it has spread within the breast or to other parts of the body. Doctors use a cancer’s stage as a key factor in making treatment recommendations and estimating a patient’s chance for recovery.
To figure out the stage, doctors may use imaging tests such as mammograms, ultrasounds, chest x-rays, bone scans, computed tomography (CT) scans, magnetic resonance imaging (MRI) scans, and positron-emission tomography (PET) scans, as well as tests of tissue samples (biopsies). Your team will explain which tests you need, what to expect, and what the results mean.
There are two main systems for determining the stage of breast cancer.
- TNM staging: TNM is an acronym of the words tumor, nodes, and metastasis. This system describes breast cancer in terms of the size of the original tumor, whether any lymph nodes are involved, and whether the cancer has metastasized, or spread from the breast to another part of the body.
Overall stage grouping: Once TNM is determined, a stage is assigned using overall stage grouping, also known as Roman-numeral staging. This system uses the numerals 0, I, II, III, and IV to describe the progression of cancer, with 0 being precancerous changes or noninvasive cancers and IV being the most advanced stage. The following terms are used loosely to refer to these stages:
- Noninvasive cancers are at stage 0.
- Early-stage cancers are at stages I and II, and sometimes III.
- Advanced cancers are at stages III and IV.
- T - tumor size: The letter T followed by a number from 0 to 4. A higher T number means the tumor is larger, has spread more widely into nearby tissues, or both.
- N - nearby lymph nodes: The letter N followed by a number from 0 to 3. A higher N number means greater spread of cancer cells to lymph nodes near the breast, such as in the armpit (axilla) or under the collarbone (clavicle).
- M - metastasis: The letter M followed by a 0 or 1. M0 means a physical exam and imaging studies, such as X-rays, have not found cancer in lymph nodes away from the breast or in distant organs; M1 means distant spread was found.
Overall Stage Grouping
- Stage 0: Noninvasive cancers (ductal carcinoma in situ, or DCIS, and lobular carcinoma in situ, or LCIS) are considered stage O.
- Stage I: The tumor is smaller than 1 inch, and the cancer has not spread to the lymph nodes under the arm or to other sites beyond the breast.
- Stage II: The tumor is 1 to 2 inches in size, or the cancer has spread to the lymph nodes under the arm. Stage I or II cancers may be called early-stage cancers.
- Stage III: This is a more advanced cancer, but it is still confined to the breast, surrounding tissues, and lymph nodes. Stage III cancers may be considered early-stage or advanced cancers.
- Stage IV: The breast cancer has spread or metastasized to distant sites, such as the lungs, liver, bones, and brain, or to lymph nodes outside of the underarm area.