Breast cancer staging is a way to classify breast tumors once they have been diagnosed. The stage of a breast tumor can indicate how advanced it is and help determine what treatment(s) may be appropriate and what the patient and doctor can expect.

Breast surgeon Hanh-Tam Tran explains how the categories are calculated and what the numbers may mean for your treatment and prognosis.

How do doctors stage breast cancer?

Staging breast cancers is complex, and considers different types of information gathered from:

• Tests and imaging, such as blood tests, mammograms, ultrasound, MRI, CT scans and PET scans.
• Biopsy results, which can reveal clinical features to determine the aggressiveness of cancer cells.
• Genetic profiling of cancer cells to look for characteristics that may make them respond to particular forms of medical treatment.
• Post-surgical pathology that can see the growth patterns of tumors and gauge their invasiveness.

What are the stages of breast cancer?

Breast cancer staging uses Roman numerals 0, I, II, III and IV, with 0 being noninvasive cancer cells in one spot (in situ) and IV being invasive breast cancer that has spread into other areas of the body. The five numerals have A and B subcategories that look at other factors such as lymph node involvement and metastases (areas of spreading cancer).

The American Joint Committee on Cancer uses the letters T, N and M to characterize three different aspects of breast tumors.

T: Tumor

This designation looks at the tumor, its size and whether or not the cancer has invaded surrounding tissue.

The “T” designation has several categories:

• TX means the tumor is not assessed.
• T0 means there is no evidence of invasive breast cancer.
• T1, T2 and T3 refer to the size of the tumor and consider if and how far it has invaded surrounding breast tissue.

N: Nodes

• An important aspect of staging breast cancer has to do with whether the cancer has spread to one or more nearby lymph nodes — fluid channels in the breast. The “N” value describes if and how the cancer has infiltrated one or more lymph nodes near the breast. NX means lymph nodes have not been evaluated.
• N0 means there is no cancer detected in the nearby lymph nodes.
• N1, N2 and N3 mean that breast cancer is in the lymph nodes. The higher the number, the more advanced the lymph node involvement. “These cancers have an increased risk of spreading beyond the breast to lymph nodes and to other organs within the body,” says Tran.

M: Metastasis

M stands for metastasis, and measures if and how far the breast cancer has spread to other parts of the body.

• MX means spread cannot be determined.
• M0 means no distant metastasis is present.
• M1 means the breast cancer has metastasized to other areas of the body.

What other factors go into staging breast tumors?

Here are some other breast cancer characteristics that go into staging.

Tumor grade: Grade refers to how abnormal the cancer cells are. A pathologist looks at the cancer cells under a microscope. The more the cancer cells resemble healthy cells, the lower the grade. Very abnormal cancer cells may be faster growing or more likely to spread.

Hormone receptor status: Cancer cells can have hormone receptors that make them more likely to respond to hormone therapy.

Tran explains, “Your pathology report will determine if your cancer is estrogen receptor (ER) positive or negative, or progesterone receptor (PR) positive or negative. Positive hormone receptive cancers are more likely to respond to anti-estrogen therapies, like tamoxifen or an aromatase inhibitor. Hormone negative cancers may respond to other types of treatments.”

HER2 status: A breast cancer cell’s DNA can reveal more about how aggressively the cancer can grow or spread. HER2 is a cancer gene that creates extra HER2 protein receptors in some breast cancers, which are known as HER2+, or HER2 positive, disease.

“While HER2+ cancer can be aggressive, biologic targeted therapies such as trastuzumab can treat it successfully,” Tran says.

Genomic test score (such as Oncotype DX): a calculation, based on the cancer cells’ genetic makeup, that helps your doctor predict how fast the cancer is likely to grow and return after treatment.

Since preventing or stopping the spread of breast cancer is your care team’s main objective, it is helpful to understand the genetic characteristics of breast cancer cells: They do not all “behave” the same way.

“Studying the cells of a breast tumor can reveal how and how quickly they are growing and spreading. Certain genetic characteristics signal cancer cells that are more likely than others to come back,” Tran says.

What does breast cancer staging mean for my prognosis?

Most people confronting breast cancer are concerned about what the future will hold — their prognosis. It’s understandable to be concerned: Will the treatment be effective? Can you expect a shortened lifespan?

Staging the breast cancer can put a number to a tumor’s characteristics and behavior, but these are only parts of your entire prognosis. Your overall health matters, too.

It’s important to remember that breast cancer stage is not fixed. “Your breast cancer stage can improve with treatment,” Tran says. “For instance, if the tumor responds to endocrine therapy or chemotherapy, the grade can actually go down.”

Your surgeon, oncologist and primary care provider can discuss each step of your treatment with you and give you an idea of what to expect. Tran says that, whereas generations ago, a particular breast cancer stage was associated with a high or low five-year survival probability, the outlook is vastly different today.

“Most people with breast cancer live beyond five years, and with successful treatment, it is possible to live many years and eventually die from other causes. And, continuing advancements in diagnosis and treatment offer hope for the future.”