Understanding Breast Cancer Staging and Grading: A Pathology Perspective

By: Heba Khan, BS and Renee Frank, MD

Being told you have breast cancer can feel overwhelming. Doctors often mention the “stage” and “grade” of the cancer, but these words may be unfamiliar. Understanding

what these terms mean can help you feel more informed and involved in your care.

What Do Grade and Stage Mean?

• Grade describes how the cancer cells look under a microscope, as seen by a pathologist. Grade shows how different the cancer cells are from normal breast cells and how quickly they are likely to grow.

• Stage describes how far the cancer has spread in the body. This includes the size of the tumor in the breast, whether it has spread to nearby lymph nodes, and whether it has reached other organs.

Both grade and stage are important in guiding treatment decisions between you and your medical and surgical team.

Grading the Cancer

When a biopsy or surgical sample is examined under the microscope, the pathologist assigns a grade:

• Grade 1 (low grade): Cells look more like normal breast cells and usually grow slowly.

• Grade 2 (intermediate grade): Cells look somewhat different from normal and

usually grow at a moderate pace.

• Grade 3 (high grade): Cells look very different from normal and are more likely

to grow and spread quickly.

The grade helps doctors understand how aggressive your cancer may be.

How Do Pathologists Examine Your Tissue Under the Microscope?

A biopsy specimen is a sample of tissue that is removed from the area that needs

microscopic examination and pathologic diagnosis. The tissue is usually obtained from

the breast and/or from neighboring lymph nodes. Core needle biopsies of the breast

and neighboring tissue are often performed by a radiologist or surgeon for initial

diagnosis. Once the tissue/biopsy sample is procured, the tissue is placed in a

preservative (formalin). Formalin fixation is done to stabilize the cells for processing.

Pathologists review the sample in two different ways: a gross inspection and a

microscopic review. Gross inspection includes physical description: meaning the size, color, and any visible abnormalities. Once the gross examination is complete, the tissue is processed and cut into very thin slices (about 4 microns thick). These sections can be

further processed with dyes that help with visualizing parts of cells and other structures.

Fixation and staining provide maximum detail of the tissue for proper examination under

a microscope. Microscopic examination looks at the appearance of the cells that helps

provide a benign diagnosis, which is typically normal or a self-limiting cell growth, or a

cancer diagnosis which is classified under the grading criteria mentioned above. Lastly,

the slides can be saved and analyzed in the future if needed.

TNM Staging System

Doctors and pathologists use the TNM system to describe breast cancer (as well as

other cancers) based on the physical location of cancer growth in the body.

• T (Tumor): The size of the main tumor and if it has grown into nearby tissues of

the same organ.

o Tis: “In situ,” meaning the cancer has not grown into deeper breast tissue.

o T1-4: The greater the size of the tumor, the larger the T number.

• N (Nodes): Whether the cancer has spread to nearby lymph nodes.

o N0: No cancer in nearby lymph nodes.

o N1-3: Cancer in lymph nodes in various locations, the farther the lymph

node from the breast, the higher the N number.

• M (Metastasis): Whether the cancer has spread to other parts of the body.

o M0: No spread beyond the breast area.

o M1: Cancer has spread to distant organs (such as lungs, liver, or bones).

By combining T, N, and M, doctors assign an overall stage (I through IV). Generally,

higher numbers mean the cancer and its spread is more advanced.

Why This Matters

In their reports, pathologists provide a diagnosis based on gross description,

microscopic description, radiologic findings, and clinical findings (ie the triple test). This

information helps guide treatment decisions, which may include surgery, radiation,

chemotherapy, hormone therapy, or a combination.

Summary

Understanding the grade and stage of breast cancer is essential for making informed

decisions about your care. Grade tells us how abnormal and fast-growing the cancer

cells are, while stage shows how far the cancer has spread. Pathologists play a key role

in diagnosing and classifying breast cancer by examining tissue samples under the

microscope. Together, this information helps you and your medical team choose the

most effective treatment plan for you.