Understanding Metastatic Breast Cancer

A diagnosis of metastatic breast
cancer (MBC) can be overwhelming.
Learning more about the disease
can help you cope and make
decisions for improving your
overall quality of life.

Defining MBC

When breast cancer metastasizes, that means it has spread to other places in your body outside of the breast. Whether the cancer spreads to the bones, lungs, liver, or another place, it is still considered breast cancer. This is because these metastases have the same type of cancer cells as the primary cancer located in the breast.


MBC is sometimes referred to as advanced breast cancer or Stage 4 breast cancer. It is important to note that while “Stage 4 breast cancer” is commonly used interchangeably with “MBC,” the 2 terms do not always mean the same thing. The stage is determined at or soon after diagnosis, based on whether the cancer is limited to 1 area of the breast or whether it has spread to other areas or organs at said time. Over the course of the disease, your stage will most likely remain the same, even when the disease becomes metastatic. This means that you can have Stage 2 breast cancer and still have metastatic disease.

Incidence of breast cancer in the United States

Breast cancer is the most common cancer among women in the United States (excluding cancers of the skin). As of January 1, 2019, there were more than 3.8 million women living in the US who had been diagnosed with breast cancer at some point in their lives. The number of women diagnosed with or living with MBC, however, is not currently measured. This makes it difficult to measure survival rates in MBC.

Types of treatment

Although researchers continue to study MBC, there is currently no cure. For now, the goals of treatment include extending life, reducing the symptoms of the disease, and improving quality of life. Treatment with the goal of improving quality of life is also referred to as palliative care.

MBC treatments vary for each patient. Treatment decisions are made based on specific disease characteristics, including MBC subtypes. These subtypes have specific receptors, which can tell your cancer to grow. Receptors include

  • Estrogen receptor (ER)
  • Progesterone receptor (PR)
  • Human epidermal growth factor receptor 2 (HER2)

Patients whose cancers have estrogen and/or progesterone receptors are said to have ER-positive and/or PR-positive disease. They are often treated with hormone therapy. Over time, MBC will become resistant to this type of treatment and will then likely be treated with chemotherapy.

Patients whose cancers have HER2 receptors are said to have HER2-positive disease. Patients with HER2-positive disease are treated with targeted therapies that work against the HER2 receptor with the goal of extending life. Treatment may also include chemotherapy.

Patients with triple-negative disease, or those whose cancer is negative for ER, PR, and HER2, are typically treated with chemotherapy from the beginning.

Everyone living with metastatic breast cancer will have their own individual experience with diagnosis, treatment, and day-to-day life. It is important to educate yourself and find your own support system to help you on your journey.

Working with your health care team

Because your experience with MBC is different from everyone else’s, it is important to keep the lines of communication open between you and your health care team. This includes reporting to them any and all symptoms and side effects—not only physical, but emotional, as well. Understanding your unique situation will help you to be an informed participant in your treatment decisions. By advocating for yourself, you can better understand your disease and the treatment options that are available.

Learning more

Throughout MBCInfoCenter℠, you can find additional information, support, and resources about MBC. Topics include everything from treatment information to tips about your day-to-day living. You will also find information about support groups and advocacy groups.