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.

Who’s at Risk for Developing Metastatic Breast Cancer?

Most often, metastatic breast cancer arises months or years after a person has completed treatment for early or locally advanced breast cancer. “Anyone who has early stage breast cancer is theoretically at risk for metastatic disease,” says Dr. Tiersten. “But there’s really been a paradigm shift in terms of understanding that it’s the biology of the disease, more than an exact size or positive number of lymph nodes, that increases the risk of developing distant metastases.”

The risk of metastasis after initial breast cancer treatment depends greatly on the biology of the tumor, the stage at the time original diagnosis, and the how the initial cancer was treated (trying to prevent recurrence).

How Is Metastatic Breast Cancer Diagnosed?

After a person has completed treatment for early or locally advanced breast cancer, they’ll likely come in for follow-up appointments every three months in the first year, and every six months after that.

“[Looking for] metastatic breast cancer is very symptom driven,” says Dr. Tiersten. Symptoms of metastatic breast cancer depend on where the cancer has spread. If it’s spread to the brain, for instance, a woman might have behavioral changes, seizures or headaches. If the cancer has spread to the liver, she might get jaundice, abdominal pain, or have an itchy rash.  

“[During the follow-up appointment] we do a very careful history about any new symptoms they might be having as well as a physical exam,” says Dr. Tiersten. “So, it could be something we find on physical exam. For example, if someone has lung metastases with fluid around the lung you can hear that with a stethoscope.”

It’s usually not recommended to do routine blood work or routine scans to find metastatic breast cancer during a patient’s follow-up appointments, Dr. Tiersten says. “That’s really because it’s never shown to be helpful,” she says.

How Is Metastatic Breast Cancer Treated?

While metastatic breast cancer can’t be cured and is more difficult to treat than early-stage breast cancer, there are many treatment options available. “Metastatic breast cancer used to be considered a death sentence and that’s absolutely not true anymore,” says Dr. Tiersten. “We think of it as a chronic disease.”

When breast cancer metastasizes, or spreads to different parts of the body, it is still considered breast cancer and is treated as such. The metastatic tumor is the same type of cancer as the primary tumor. For example, if the cancer has spread to the bones, it is still treated with breast cancer drugs because they are breast cancer cells.

The most common treatments for metastatic breast cancer in any location are systemic medications, which aim to treat cancer throughout the entire body. Systemic medications include:

• Chemotherapy
• Hormonal therapy
• Targeted therapy
• Biologic therapy

The treatment strategy for metastatic breast cancer is guided by many factors, including the characteristics of the cancer cells, where the cancer has spread, past breast cancer treatments, and the patient’s symptoms and lifestyle needs.

“Patients with metastatic breast cancer can live good quantity and quality of lives, we have great treatment for it. Patients are living sometimes without evidence of disease for many years more and more,” says Dr. Tiersten.