Staging is a complex process used by physicians to determine how much cancer a patient has and which parts of his or her body are affected. In addition to its extent and location, breast cancer is classified based on its genetic makeup, its sensitivity to certain hormones and whether it tests positive for specific proteins that can promote its growth.
After evaluating these factors, a physician can assign a stage to breast cancer. The physician may then use this information to describe the cancer, determine the patient’s prognosis and plan treatment.
How is breast cancer staged?
Breast cancer staging typically begins with a physical examination, imaging scans and a biopsy of a tumor tissue sample. The most common method of staging breast cancer uses the TNM system, which involves an analysis of three key measures:
- T – Tumor size
- N – Lymph node status (the number and location of any cancerous lymph nodes)
- M – Metastasis (whether or not the cancer has spread to other parts of the body)
When using the TNM system for breast cancer staging, a physician will consider several additional factors, including:
The grade of the tumor
When examining the tissue sample under a microscope, a pathologist will visually compare the breast cancer cells to healthy cells, then assign a tumor grade based on the degree of similarity between them (the more the cancerous cells resemble normal cells, the lower the grade assigned). Additionally, the pathologist will determine the number of cancerous cells that are in the process of dividing. If relatively few breast cancer cells are dividing, the tumor is generally considered to be slow-growing and may be downgraded.
The tumor grades used to classify breast cancer are:
- Grade 1 – The cancerous cells look relatively normal and the tumor is slow-growing (well-differentiated).
- Grade 2 – The appearance and division rate of the cancerous cells fall somewhere in between grade 1 and grade 3 (moderately differentiated).
- Grade 3 – The cancerous cells have a very abnormal appearance and the tumor is fast-growing (poorly differentiated).
The hormone receptor status of the tumor
Some types of breast cancer are fueled by certain hormones produced naturally by the body, such as estrogen and progesterone. These breast cancer cells have special proteins (hormone receptors) on their surface. After binding to the hormone receptors, the hormones can accelerate the growth of the tumor.
When performing a biopsy, a pathologist can test the tumor tissue to determine its hormone receptor status. The breast cancer will be classified as estrogen-receptor-positive (ER+) if it has receptors for estrogen, which suggests that the cancerous cells, like healthy breast cells, may receive signals from estrogen that could promote their growth. Likewise, the breast cancer will be classified as progesterone-receptor-positive (PR+) if it has receptors for progesterone.
The HER2 status of the tumor
Human epidermal growth factor receptor 2 (HER2) is a protein found on the surface of some breast cancer cells. HER2 plays an integral role in the growth and survival of the cancer cells. During a biopsy, a pathologist can test the tumor sample for HER2; if this protein is detected, the cancer is classified as HER2-positive breast cancer.
The staging scale for breast cancer
Based on a comprehensive evaluation of the above factors, the physician will assign a stage to the cancer. Breast cancer is staged based on a numerical scale that ranges from 0 to 4:
Stage 0 breast cancer
At stage 0, breast cancer is noninvasive and confined to the lining of the milk ducts or breast lobes (ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS), respectively). There is no evidence that precancerous cells or breast cancer cells have invaded nearby healthy tissues.
Stage 1 breast cancer
At stage 1, breast cancer cells have spread from the milk ducts or lobes into the surrounding breast tissues but remain contained within a relatively small area. The cancer is classified as stage 1A if the breast tumor is smaller than 20 mm in diameter (the size of a grape) and has not spread to nearby lymph nodes.
The cancer is classified as stage 1B if small clusters of breast cancer cells are found in nearby lymph nodes and:
- The breast tumor is larger than 20 mm in diameter; or
- There is no breast tumor, but cancerous cells in the breast tissues have formed clusters that are between 0.2 and 2 mm in diameter.
Stage 2 breast cancer
At stage 2, breast cancer is locally invasive and growing, but still contained within the breast and/or the surrounding lymph nodes.
The cancer is classified as stage 2A if:
- The breast tumor is smaller than 2 cm in diameter and breast cancer cells are found in the lymph nodes in or around the armpit (axillary lymph nodes); or
- The breast tumor is between 2 and 5 cm in diameter but breast cancer cells have not spread to the axillary lymph nodes; or
- There is no breast tumor, but cancerous masses larger than 2 mm in diameter are found in up to three axillary lymph nodes.
The cancer is classified as stage 2B if:
- The breast tumor is between 2 and 5 cm in diameter and breast cancer cells have spread to up to three axillary lymph nodes; or
- The breast tumor is larger than 5 cm in diameter but breast cancer cells have not spread to the axillary lymph nodes; or
- There is no breast tumor, but a tumor in a nearby lymph node is between 2 and 5 cm in diameter and other breast cancer cells have formed clusters that are between 0.2 and 2 mm in diameter.
Stage 3 breast cancer
At stage 3, the breast cancer is regionally invasive and has spread beyond the breast tissue and nearby lymph nodes, but has not reached distant tissues or organs.
The cancer is classified as stage 3A if:
- The breast tumor is larger than 5 cm in diameter and breast cancer cells in the lymph nodes have formed clusters that are between 0.2 and 2 mm in diameter; or
- The breast tumor is larger than 5 cm and breast cancer cells have spread to up to three axillary lymph nodes; or
- There is no breast tumor, but a tumor is growing alongside breast cancer cells in four to nine axillary lymph nodes.
The cancer is classified as stage 3B if a breast tumor of any size has spread into the chest wall or breast skin and up to nine axillary lymph nodes.
The cancer is classified as stage 3C if there is no breast tumor or a breast tumor of any size has spread into the chest wall or breast skin, and breast cancer cells have spread to 10 or more axillary lymph nodes.
Stage 4 breast cancer
At stage 4, breast cancer is metastatic and has entered the lymphatic system or bloodstream and spread to distant tissues or organs, such as the lungs, liver, bones or brain.
Getting medical help for any stage of breast cancer
The multispecialty team in the Don & Erika Wallace Comprehensive Breast Program at Moffitt Cancer Center offers the latest treatment options for all stages of breast cancer. For information about our evidence-based techniques and individualized treatment approach, please call 1-888-663-3488 or complete our new patient registration form form online.