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How Does Breast Cancer Metastasize?

Learn how cancer cells spread from tumors in the breasts to other locations in the body.

Hand holding a microscope slide

Medically reviewed in November 2021

“Metastasis” is the term used to describe the spread of cancer from a primary tumor site to other areas of the body. Any type of cancer can metastasize, including breast cancer. When cancer begins in the breasts and spreads to other areas of the body, this is called metastatic breast cancer, or MBC.

The vast majority of people with MBC are women. The disease is very rare among men, though it does happen.

How does breast cancer metastasize?
Cancer spreads when cells break away from the primary tumor and move to other areas of the body. With MBC, this process typically begins with cancer cells from the tumor in the breast moving through the blood vessels or the axillary lymph nodes, which are located in the armpits. Lymph nodes are part of the body’s lymphatic system, a major component of the immune system that produces white blood cells and transports them throughout the body.

Cancer cells can form secondary tumors in the lymph nodes. They can also travel through the bloodstream or lymphatic system to other locations in the body, where they can continue to reproduce, forming additional secondary tumors. Although breast cancer cells may spread to any part of the body, the most common locations for metastases are the lungs, bones, liver and brain.

Because oncologists name cancer based on the primary site of origin, breast cancer that spreads to other areas of the body is still called breast cancer—just as cancer that begins in the lungs and spreads to another location in the body is still lung cancer, and prostate cancer that spreads to another location in the body is still prostate cancer.

Diagnosing metastatic breast cancer
While metastatic breast cancer refers to any breast cancer that has spread to other locations in the body, the disease is somewhat different for every patient. A diagnosis must take into account a number of factors and variables about that specific type of cancer. These include information about the parts of the body the cancer has spread to, the size of the tumors and the biology of the cancer cells, including whether they use certain hormones or proteins to fuel growth.

These factors will determine a precise diagnosis of the MBC, including the cancer stage and the grade of cancer cells. Grading is a system used to describe how abnormal cancer cells look in comparison to normal cells.

These factors will also be used when deciding on a treatment plan. While there is no cure for MBC, there are numerous treatment options available, which are helping more patients live longer, better lives while managing the disease.

Article sources open article sources

National Cancer Institute. “Metastasis.” 2020. Accessed on August 7, 2020.
National Cancer Institute. “Axillary Lymph Node.” 2020. Accessed on August 7, 2020.
National Cancer Institute. “Tumor Grade.” 2020. Accessed on August 7, 2020.
National Cancer Institute. “Study estimates number of U.S. women living with metastatic breast cancer.” May 18, 2017.
UpToDate. “Breast cancer in men.” July 2020. Accessed on August 7, 2020.
UpToDate. “Patient education: Breast cancer guide to diagnosis and treatment (Beyond the Basics).” July 2020. Accessed on August 7, 2020.
Susan G. Komen Foundation. “Metastatic Breast Cancer.” Updated May 14, 2020. Accessed on August 7, 2020.
Cancer.net. “Breast Cancer - Metastatic: Statistics” January 2020. Accessed on August 7, 2020.
Cancer.net. “Breast Cancer - Metastatic: Diagnosis.” April 2019. Accessed on August 7, 2020.
Cancer Research UK. “How cancer can spread.” July 6, 2020. Accessed on August 7, 2020.
American Cancer Society. “Understanding Advanced Cancer, Metastatic Cancer, and Bone Metastasis.” December 15, 2016. Accessed on August 7, 2020.
National Breast Cancer Foundation. “Metastatic Breast Cancer.” 2020. Accessed on August 7, 2020.
Science Daily. “Breast cancer’s spread routes mapped.” February 27, 2018.

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