Everything You Need to Know About Metastatic Breast Cancer

Metastatic breast cancer (MBC) happens when breast cancer spreads to other parts of the body, but unlike a new diagnosis, metastatic breast cancer is usually a recurrence of breast cancer. According to Marisa Weiss, M.D., the founder and chief medical officer of Breastcancer.org, and a breast radiation oncologist from Wynnewood, PA, most cases of MBC are experienced by people who have had breast cancer in the past. In fact, only 6% of patients are initially diagnosed with metastatic breast cancer.

Let’s take a look at metastatic breast cancer in more detail, including its symptoms, diagnosis, and treatment.

“Metastatic breast cancer refers to cancer that has spread from its original location [the breast] to other parts of the body,” explains Lynn Symonds, M.D., a medical oncologist at the Fred Hutchinson Cancer Center and a clinical researcher in medical oncology at the University School of Medicine in Seattle, WA.

When breast cancer spreads or metastasizes to other areas of the body, it is still considered breast cancer. For instance, if breast cancer spreads to the lungs, it remains breast cancer that has metastasized to the lungs, not lung cancer itself.

There are different terms used to describe metastatic breast cancer depending on the circumstances. If you had a prior breast cancer diagnosis and it returns in a distant location, it is referred to as a distant recurrence. On the other hand, if your initial diagnosis is metastatic breast cancer, it is called de novo metastatic breast cancer. Metastatic breast cancer is also known as stage four or advanced breast cancer.

Of the more than 150,000 people in the United States living with metastatic breast cancer, three-fourths were originally diagnosed with an earlier stage of cancer, according to the American Cancer Society.

The number of people living with metastatic breast cancer is estimated to grow to nearly 170,000 by 2025, according to a study published in the Journal of the National Cancer Institute. That’s not necessarily bad news: The number is increasing partly due to better diagnostics and people living longer with MBC due to systemic treatment advances.

While MBC is often a recurrence of previous breast cancer, certain factors can increase the likelihood of the cancer spreading to other parts of the body. By identifying these risk factors, your doctor can provide targeted interventions and support, potentially improving outcomes and quality of life. These are the main risk factors to be aware of, according to the American Society of Clinical Oncology:

• Previous diagnosis of breast cancer: This is the biggest risk factor for MBC. Nearly 30% of patients diagnosed with early-stage cancer will develop metastatic breast cancer at some point, according to a review in the Journal of Internal Medicine. Any kind of breast cancer can metastasize, although some types are more likely to return than others.

• Type and severity of initial breast cancer. The attributes of an initial breast cancer diagnosis can put you a higher risk for metastasis. A more advanced initial diagnosis—for example, a large tumor or significant lymph node involvement—can increase your risk for metastatic breast cancer, Dr. Weiss says.

• Untreated breast cancer: Having breast cancer that hasn’t been treated can put you at risk of presenting initially with metastatic breast cancer, says Dr. Symonds. This occurs when patients, for example, notice a breast mass but don’t seek treatment for a significant amount of time.

Because metastatic breast cancer is still breast cancer, it has the same subtypes as any breast cancer. By subtyping a cancer, physicians are better able to give a prognosis, treat, and research the cancer. The main subtypes according to the Journal of Clinical Oncology are:

• Hormone-receptor positive: Breast cancers that have estrogen and/or progesterone receptors are called hormone-receptor positive. These cancers may depend on estrogen and/or progesterone to grow. Breast cancer may be estrogen-receptor positive and/or progesterone-receptor positive.

• HER2-positive: Breast cancers that rely on the gene called human epidermal growth factor receptor 2 (HER2) to grow are called HER2-positive. HER2-positive breast cancers can be hormone-receptor positive or negative.

• Triple-negative breast cancer: If a breast cancer is estrogen-receptor negative, progesterone-receptor negative, and HER2 negative, it’s called triple-negative. This type of tends to grow and spread faster than other types.

When breast cancer metastasizes, cancer cells break away from the breasts and nearby lymph nodes and travel through the blood or lymph system to form tumors in other parts of the body. Not all breast cancers spread in the same way or at the same speed for each person. According to the National Cancer Institute, cancer cells can move from the breast to other areas in the body through these pathways:

• Local Invasion: Breast cancer typically starts in the milk ducts and lobules. But as it progresses, it can invade nearby healthy tissues, including the surrounding breast tissue or the lymph nodes located in the underarm area.

• Lymphatic Spread: The lymphatic system consists of a network of vessels and lymph nodes that help drain excess fluid and waste products from the body. Breast cancer cells can enter the lymphatic vessels and travel to nearby lymph nodes, and then continue to spread to other lymph nodes.

• Hematogenous Spread: Breast cancer cells can enter the bloodstream and travel to distant organs. The exact mechanisms by which cancer cells interact with blood vessels and organs to establish new tumors are complex and still being studied.

But where do these rogue cancer cells go? They can go anywhere, really, but according to the American Society of Clinical Oncology, the most common places for breast cancer to spread to include:

• Lymph nodes

• Bones

• Lungs

• Brain

• Liver

Symptoms of metastatic breast cancer depend on the part of the body where the breast cancer has metastasized and how much it has spread. MBC can also be asymptomatic, where you have no symptoms or side effects at all.

“Pain can be a symptom, particularly if it’s in the bones,” says Dr. Symonds. Lower back pain that’s persistent and gets progressively worse, for example, may be a symptom of metastasis to the bone. However, many symptoms of metastatic breast cancer have other common causes as well, so it’s always important to talk to your doctor about your concerns.

The American Society of Clinical Oncology recommends that you discuss the following symptoms with a doctor (grouped by the areas of the body they typically relate to):

• Bone metastasis symptoms: Bone, back, neck, or joint pain; bone fractures; swelling

• Brain metastasis symptoms: Headache; nausea; seizures; dizziness; confusion; vision changes, such as double vision or loss of vision; personality changes; loss of balance

• Lung metastasis symptoms: Shortness of breath; difficulty breathing; constant dry cough

• Liver metastasis symptoms: Yellowing of the skin and whites of the eyes, called jaundice; itchy skin or rash; pain or swelling in the belly; loss of appetite; nausea

• Other symptoms of metastasis: Loss of appetite; weight loss; nausea; vomiting; fatigue

Dr. Weiss explains that most diagnoses of metastatic breast cancer (MBC) occur when a person who had breast cancer before experiences new and concerning symptoms. These symptoms usually develop gradually, persist over time, and may worsen.

During the follow-up phase after completing treatment for the original breast cancer, regular check-ups with your cancer doctor become essential. Typically, you will have annual visits where your doctor will assess your overall health. If you have any unusual physical findings or unexplained symptoms, your doctor may order lab tests and imaging scans to determine if the cancer has returned and if it has spread to other areas of the body.

If necessary, your doctor may recommend a biopsy, which involves taking a small sample of tissue for examination. Biopsies are considered the gold standard for diagnosing any form of cancer. They not only confirm the diagnosis but also provide important information about the type of cancer cells found, helping doctors make more accurate decisions about treatment options.

Metastatic breast cancer is not considered curable, but it is treatable. “Once the cancer has spread beyond the breast and the nearby lymph nodes, it’s systemically within the body,” says Candice Thompson, M.D., a breast surgeon at Stanford Medicine and an assistant professor at the Stanford School of Medicine Department of Surgery in Stanford, CA. “There’s always some microscopic level of cancer in the body, even if the scans show that it’s negative.”

To be clear, metastatic cancer is different from terminal cancer. Terminal cancer occurs when no more treatment options are effective against a cancer, and treatment focuses on comfort instead. The aims of treatment for metastatic cancer are to get the cancer under control and keep it from growing and spreading further.

“We see it as more of a chronic problem that requires ongoing treatment, that hopefully we can get under control and in remission, so it doesn’t interfere with your everyday life,” says Dr. Weiss. “Or, if it does cause issues in your everyday life, we to try to minimize that.”

The treatment goal with MBC is to manage the cancer, limit its spread, and put it into remission. Although there are exceptions, generally, eradicating the cancer completely is usually not possible. A typical pattern is to use a treatment for as long as it works and is tolerable, before moving on to the next treatment, says Dr. Thompson.

Treatment decisions also balance effectiveness with side effects and quality of life. “It really is about trying to tailor things to the individual patient to help find the best treatment approach,” Dr. Symonds says.

MBC treatment choices depend on many factors, including the subtype of breast cancer, the location and extent of the metastasis, your response to previous treatments, and any genetic mutations, as well as side effects, your overall health, and other health conditions.

Because MBC is a systemic condition (a.k.a. a condition that affects your whole body), “we normally focus on using systemic therapies that are going to treat the whole body,” says Dr. Symonds. Examples of systemic therapies include:

• Chemotherapy: Chemotherapy is often used to treat all three subtypes of MTB—HER2-positive, hormone-receptor positive, and triple-negative breast cancer.

• Hormonal therapy: Hormone-blocking drugs are used for cancers that test positive for hormone receptors.

• Immunotherapy: Immunotherapy boosts the body’s natural defenses to fight the cancer. It may be used to treat cancer with a specific gene mutation, for example.

• Targeted therapy: Targeted drugs are used to treat HER2-positive and hormone-receptor positive breast cancer.

Depending on the location and characteristics of the metastasized cancer, treatments may be combined or used locally with radiation or surgery.

“Normally people stay on a treatment until either their cancer stops responding to it or they have side effects that tell us that that might not be the right treatment for them,” says Dr. Symonds. “But normally, treatments are ongoing, because the goal is to control the cancer.”

Clinical trials are also an option. “In addition to standard treatments, it can also be exciting and empowering for patients to participate in research studies,” says Dr. Symonds.

“There’s constant research ongoing to find new therapies,” says Dr. Symonds. “Even in the last year, multiple new therapies have been FDA approved for the treatment of metastatic breast cancer.

There’s no way to predict how long an individual will live with MBC. According to researchers at the American Society of Clinical Oncology, the five-year survival rate for women with metastatic breast cancer in the United States is 30%, and the five-year survival rate for men is 19%. That said, one-fifth of individuals diagnosed with metastatic breast cancer are estimated to have been living with metastatic disease for 10 or more years.

The expanded range of treatment options has improved survival rates for metastatic disease. “The survival rate has significantly increased over the last few decades due to better targeted therapies,” says Dr. Thompson.

Many people—and increasingly so—can live with MBC for many years. Some people continue to work through their MC diagnosis. But quality of life is highly individualized. Your response to treatment, side effects, and your overall health will affect how you feel and what you can comfortably do.

“We’re not only trying to prolong life, but we’re also trying to improve quality of life with the treatment,” says Dr. Symonds.

While your medical treatment will likely have a large influence on your quality of life, other factors such as social support and mental health also factor in. Dr. Symonds recommends asking your provider about support services and resources.

“The ultimate goal of the breast cancer community is to continue to do research to help people live even longer and even better and to create better therapies,” says Dr. Symonds. “And of course, we’re all working very hard towards that.”