What Is Metastatic Breast Cancer? An Oncologist Explains

What Is Metastatic Breast Cancer? An Oncologist Explains

What Is Metastatic Breast Cancer? An Oncologist Explains


Metastatic breast cancer is not a specific type of breast cancer, but rather the most advanced stage of breast cancer (also known as stage IV). The term metastatic means the cancer has spread beyond the initial site, in this case, the breast, to other parts of the body. The most common sites for metastatic breast cancer to spread are the bones, lungs, liver, lymph nodes, and sometimes the brain.

It’s estimated that at least 154,000 people in the U.S. have metastatic breast cancer. Some women have metastatic breast cancer when they are first diagnosed (called de novo metastatic breast cancer), but it’s uncommon. “About 10% of breast cancers present initially with metastatic disease, but the majority of patients present with early stage breast cancer,” says Amy Tiersten, MD, a hematologist and oncologist at the Mount Sinai Hospital in New York City. While many cases of early stage cancer can be cured, in some instances the cancer can come back years later as metastatic breast cancer.

How Does Metastatic Breast Cancer Develop?

“The way metastatic breast cancer develops is, even when we’ve completely eradicated the tumor and given treatment for preventing recurrence, there still could be one cell that’s resistant to that treatment,” says Dr. Tiersten. “And that cell can travel and find its way to a different organ, and grow to the point where it’s detectable in one way or another.”

The spread of breast cancer usually occurs through one or more of the following ways:

Cancer cells invade nearby healthy cells. If a healthy cell has been taken over by a cancer cell, it can replicate more abnormal cells.
Cancer cells travel. Cancer cells can penetrate through walls of nearby lymph vessels or blood vessels, and then circulate through the lymph system or bloodstream to other parts of the body.
Cancer cells lodge in capillaries. If cancer cells become lodged in the capillaries (tiny blood vessels) of a distant location, they divide and migrate into the surrounding tissue.
Cancer cells form new tumors. Once cancers cells have arrived at a distant location (called micrometastases), it can cause new small tumors to grow.