Understanding the clinical staging of breast cancer

By Lauren Evoy Davis 

 Medically reviewed by Oliver Eng, MD

Cancer staging is the process of determining how much cancer is within the body (tumor size) and if it has spread. For breast cancer, this might take the form of clinical (pre-surgical) staging or pathologic (surgical) staging.

Breast cancer is classified by stages. There are five stages of breast cancer, (stages 0, 1, 2, 3, and 4). Doctors use a specific classification system, known as the TNM (tumor, node, metastasis) system to stage breast cancer and guide treatment.¹

This article explains what is involved in clinical breast cancer staging and what the different stages mean. It also explains what to expect after the clinical stage has been established.

 Verywell / Gary Ferster

Breast Cancer Tumor Size

Doctors usually measure the size of the tumor in centimeters (cm). Some common foods analogies can help to better understand tumor sizes:²

• 1 cm is about the width of a pea

• 2 cm is about the size of a peanut

• 3 cm is about the size of a grape

• 4 cm is about the size of a walnut

• 5 cm is about the size of a lime

• 6 cm is about the size of an egg

• 7 cm is about the size of a peach

• 10 cm is about the size of a grapefruit

For the clinical staging of breast cancer, your cancer specialist (oncologist) may use one or more of the following imaging tools:³

• Mammogram: This is an X-ray procedure specific to the breast.

• Breast ultrasound: This uses a non-invasive procedure that can visualize and measure a tumor using reflected sound waves.

• Breast magnetic resonance imaging (MRI): This uses powerful magnetic and radio waves to image soft tissue. It is typically employed when breast tissue is dense or a biopsy shows that the mass is larger than expected.

TNM System for Breast Cancer Staging

Breast cancer and most other solid tumor cancers are staged with a system called the TNM Classification of Malignant Tumors. The abbreviation "TNM" stands for the three characteristics used to determine the stage of cancer:⁴

• Tumor size: This refers to the size and extent of the primary (main) tumor.

• Number of lymph nodes: This is the number and location of lymph nodes with cancer in them.

• Metastasis: This indicates whether or not cancer has spread (metastasized) from the primary tumor to other parts of the body.

Based on the findings, cancer is staged from 0 to 4, with 0 being the least advanced stage and 4 being the most advanced stage. The cancer stage directs the appropriate course of treatment and predicts the likely outcome (prognosis).¹

This includes determining whether a lumpectomy (the removal of the tumor) or a mastectomy (the removal of the tumor and breast) is needed.

Clinical vs. Pathologic Staging

Clinical breast cancer staging can help direct if a lumpectomy or mastectomy is most appropriate. But for the purpose of cancer diagnosis and treatment, pathologic breast cancer staging is considered the gold standard.⁵

T Classification for Clinical Breast Cancer Staging

In the TNM system, tumor size plays a central role in clinical and pathologic staging. The extent to which the tumor has grown into surrounding tissues is also important.

Tumor size is categorized in the TNM system as follows:¹

N Classification for Clinical Breast Cancer Staging

When you have breast cancer, the cancer cells can migrate through a network of lymphatic vessels to nearby lymph nodes. The lymph nodes nearest the tumor will almost invariably have more cancer cells than those further down the line.

The number and extent of lymph node involvement are central factors for the staging of breast cancer. This primarily involves axillary lymph nodes of the armpit, but may also involve supraclavicular lymph nodes around the collarbone and mediastinal lymph nodes around the breastbone.

For the clinical staging of breast cancer, your oncologist will palpate (physically touch) areas of skin nearest the tumor to feel for lumps. The clinical staging is ultimately based on the number, size, texture, and location of swollen lymph nodes.¹

Alternatively, your lymph nodes may be evaluated with a sentinel node biopsy. This is when one or two lymph nodes nearest the tumor are removed and directly inspected for cancer cells in the laboratory.

M Classification for Clinical Breast Cancer Staging

Metastasis is the extent to which cancer has spread beyond the primary (original) tumor. When clinically staging breast cancer, a sentinel node biopsy is needed.¹

This method is not definitive proof of metastasis but is useful in determining what other procedures are needed to confirm metastasis. This includes a computed tomography (CT) scan and/or a positron emission tomography (PET) scan, both of which can pinpoint cancer cells in other parts of the body.

Breast Cancer Treatment Options

Stages of Breast Cancer

Breast cancer has five stages. Your stage is based on the TNM classification.

Stage 0

Stage 0 is used for precancer, also known as carcinoma in situ. This is when abnormal cells that look like cancer are seen under the microscope but are only found in the place where they first formed and have not spread to nearby tissues.⁶

Stage 1

Stage 1 means that cancer is small and is only in the breast tissue or possibly in the lymph nodes closest to the breath. There are two subcategories of stage 1 breast cancer:⁷

Stage 1A:

• The tumor measures up to 2 cm.
  AND

• Cancer cells have not spread out of the breast into nearby lymph nodes.

Stage 1B:

• A small cluster of cancer cells measuring 0.2 to 2 millimeters (mm) is found in nearby lymph nodes.

• A tumor may or may not be present.

Stage 2

Stage 2 is cancer that has become invasive and had spread into regional tissue. This stage also is divided into two subcategories:⁷

Stage 2A:

• There is no tumor in the breast, but a cluster of cancer cells larger than 2 mm is found in either the axillary or supraclavicular lymph nodes
  OR

• The tumor is smaller than 2 cm and has spread to nearby lymph nodes.
  OR

• The tumor measures between 2 and 5 cm and hasn't spread to nearby lymph nodes.

Stage 2B:

• The tumor measures between 2 and 5 cm and a group of cancer cells between 0.2 and 2 mm are found in the axillary lymph nodes.
  OR

• The tumor measures 2 to 5 cm, and there is cancer in up to three axillary lymph nodes.
  OR

• The tumor measures larger than 5 cm, but there isn't any cancer in the axillary lymph nodes.

Stage 3

Stage 3 cancers are invasive. This stage is divided into three subcategories:⁷

Stage 3A:

• Any size breast tumor (or no tumor) is present, and cancer has been found in four to nine axillary or mediastinal lymph nodes.
  OR

• The tumor is larger than 5 cm, and there is a small cluster of cancer cells between 0.2 and 2 mm in the lymph nodes.
  OR

• The tumor is larger than 5 cm, and cancer is found in up to three axillary or mediastinal lymph nodes.

Stage 3B:

• A tumor of any size has spread to the chest wall and/or skin with evidence of swelling or ulcers.
  AND

• Cancer has spread to up to nine axillary or mediastinal lymph nodes.
  OR

• There are skin changes suggestive of inflammatory breast cancer.

Stage 3C:

• There may be no tumor, or a tumor of any size has spread to the chest wall and/or skin.
  AND

• Cancer has spread to 10 or more axillary lymph nodes.
  OR

• Cancer has spread to supraclavicular lymph nodes above or below the collarbone.
  OR

• Cancer has spread to mediastinal lymph nodes.

Stage 4

Stage 4 is also called metastatic breast cancer.⁷ Rather than being confined to the breast and nearby lymph nodes, the cancer has traveled to other organs. It may also be a recurrence of breast cancer that has spread to other areas.

Common sites of metastases include the lungs, skin, bones, liver, brain, and distant lymph nodes.

Other Factors for Breast Cancer Staging

To better characterize the tumor you have, other tests may be performed in addition to the TNM classification. These contribute to the prognosis and treatment approach by establishing:¹

• Tumor grade: This is an examination of cancer cells to determine how aggressive (fast-growing) or indolent (slow-growing) they are.

• Hormone receptor status: These determine if you have receptors for the hormone estrogen and progesterone and whether certain targeted therapies can be used.

• HER2 status: HER2 is a protein found on some breast cancer cells that also act as a receptor for targeted drugs

After Clinical Staging

Biopsies and imaging studies give an approximate measurement of your tumor, but you need the actual tumor size in order to make the best treatment decisions.

This will involve either a lumpectomy or a mastectomy. By directly removing and examining the tumor, a surrounding margin of tissues, and nearby lymph nodes, the pathologist can provide all the information needed to accurately stage and grade your cancer.

Armed with this information, your oncologist can decide what other treatments are needed and when, including chemotherapy, radiation, hormonal therapy, or immunotherapy.

Summary

Breast cancer staging determines how much cancer is within the body (tumor size) and if it has spread. Doctors use the TNM system to stage breast cancer and guide treatment. Additional testing may be done to determine the prognosis and best treatment approach.

After the staging process, a lumpectomy or mastectomy is performed. Additional treatment may include chemotherapy, radiation, hormonal therapy, or immunotherapy.

7 Sources

American Cancer Society. Breast cancer stages.

National Library of Medicine PDQ Cancer Information Summaries. Tumor sizes.

American Cancer Society. Imaging tests to find breast cancer.

American Joint Committee on Cancer. Cancer staging system.

American Cancer Society. Understanding Your Pathology Report: Breast Cancer.

American Cancer Society. Cancer staging.

Cancer.net. Breast Cancer: Stages.

Additional Reading

Breastcancer.org 2018. Breast Cancer Stages.

National Cancer Institute 2015. Cancer Staging.

Susan G. Komen 2019. Breast Cancer Stages and Staging.

Originally written by Pam Stephan