What Is Metastatic Breast Cancer?

What to know about the most severe form of breast cancer, also known as stage 4

This article was medically reviewed by Steffini Stalos, DO, who is board-certified in Pathology and Lab Medicine, on June 27, 2022.

Breast cancer occurs when cells in the breast change and start to grow out of control, according to the National Library of Medicine MedlinePlus resource. This cancer can then metastasize (spread to other parts of the body) leading to the most severe and incurable form of the disease—metastatic, or stage 4, breast cancer.

Female breast cancer was the most commonly diagnosed cancer in the world in 2020, making up an estimated 11.7% of newly diagnosed cancer cases globally, according to data from the American Cancer Society (ACS). Male breast cancer is very rare, accounting for 1% of all breast cancer cases, per the National Cancer Institute (NCI).

The number of women living with metastatic breast cancer in the US grew to more than 150,000 cases by the start of 2017, according to a June 2017 study published in the journal Cancer Epidemiology, Biomarkers & Prevention. But, although the number of cases had increased, the survival rate doubled between 1992–1994 and 2005–2012—thanks to better screening and incredible advancements in treatment over the decades.

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What Is Metastatic Breast Cancer

Cancer cells can break away from their original location in the body and move through the blood or lymph nodes (structures in the body's immune system) to other organs to form new tumors, according to the NCI. In that case, a person may have metastatic breast cancer in another organ, most commonly bones, liver, brain, and lungs, per the ACS.

This severe form of the disease is incurable, but there are treatments that can potentially reduce symptoms and prolong lives, such as hormone therapy or chemotherapy.

Most cases of breast cancer are diagnosed in stages 1–3. Only about 6% are metastatic at diagnosis, according to NCI data from 2012-2018. From earlier stages, the disease can still metastasize, and does so in nearly 30% of cases, according to the Breast Cancer Research Foundation (BCRF). Early diagnosis is crucial.

What Causes Metastatic Breast Cancer

Breast cancer in general is caused by changes in a person's genetic material, DNA, per MedlinePlus. These can be inherited or acquired through lifestyle and environmental factors.

The cancer spreads in multiple steps. Most cancer cells die during this trip, but if conditions are "favorable" throughout, they can form new tumors, per the NCI.

This can happen regardless of whether you got diagnosed or started treatment early. Scientists are not sure why cancer metastasizes in certain patients, according to the organization Breastcancer.org.

Risk Factors

There are several risk factors for breast cancer of any stage, besides genetics. These include older age, radiation or hormone therapy, obesity, and alcohol consumption. Women who have dense breast tissue or high exposure to estrogen—a hormone for female sex characteristics, per the NCI—through their reproductive history are also at a higher risk.

There wasn't enough research on the mechanism of breast cancer metastasis, as of February 2020, when a review was published in the journal Seminars in Cancer Biology. This is because there's no one way that breast cancer metastasizes; it depends on the organs it spreads to.

Early diagnosis and treatment of breast cancer can help reduce the risk of spread, but there's no guarantee a patient can stop their cancer from progressing, per Breastcancer.org.


The symptoms of metastatic breast cancer may vary depending on where the cancer has spread in the body. Note that these symptoms can be caused by other conditions or certain medications as well, so check in with your healthcare provider. The most common signs of metastatic breast cancer, regardless of where it has spread, per the BCRF and ACS, are:

  • Fatigue or feeling weak
  • Unexplained weight loss
  • Poor appetite
  • Pain

The most common signs that depend on where the cancer has spread are:

  • Bone: New, unexplained pain in bones and joints (commonly seen in the hip or lower back), swelling, and bone fractures or breakages that appear to occur easier
  • Liver: Certain digestive symptoms such as abdominal pain, vomiting, or nausea; jaundice (a yellowing of the skin); itchy skin; and a rash
  • Lungs: Shortness of breath and cough, and chest pain
  • Brain: Headaches that persist and get progressively worse, dizziness, speech or vision problems, vomiting or nausea, seizures, behavioral changes, and memory issues

How Metastatic Breast Cancer Is Diagnosed

Diagnostic methods may vary depending on where the healthcare provider thinks the cancer may have spread. There is not one type of test that can diagnose metastatic breast cancer no matter its location. And the diagnostic tests a provider chooses may vary depending on whether a person has a history of breast cancer or not. Below are the common types of tests used to diagnose metastatic breast cancer, per Breastcancer.org:

  • Imaging tests: These can include MRI, CT, X-ray or ultrasound, or PET scans. Depending on where your provider thinks the cancer has spread, you may, say, get a bone scan or a chest X-ray.
  • Blood tests: These could show special tumor markers.
  • Biopsies: During this procedure, a person's cells or tissues are removed for examination by a specialist, per the NCI. The healthcare provider determines the suspicious areas.

In most cases, a diagnosis begins with someone with a history of breast cancer reporting a new, unusual symptom to their provider. This would prompt tests and imaging. If a former breast cancer patient says they have worsening leg or knee pain, for example, their healthcare provider might order an X-ray and bone scan to check for cancer lesions in those areas. It's important to note that not every person who has breast cancer and worsening pain in another area has developed metastatic breast cancer.

Earlier-stage breast cancer diagnosis may look different, so if a patient who doesn't have a history breast cancer comes in with symptoms, the healthcare provider may also choose to start with other tools, as well as breast-specific biopsies and blood tests. The provider would then conduct tests to determine the stage of the cancer. These initial tests can include, per MedlinePlus:

  • Physical exam: A clinical breast exam can check for unusual lumps or other signs in the breasts and armpits.
  • Medical history discussion: People can inherit the risk of breast cancer.
  • Breast-specific imaging tests: These include a mammogram, ultrasound, or MRI. Regular mammograms for women are essential no matter if they have symptoms or are at risk of breast cancer.


There is no cure for metastatic breast cancer, but there has been an increasing number of options for treatment that prolongs and improves the quality of life. The treatments for metastatic breast cancer are the same types as those used to treat earlier stages of breast cancer, per the NCI: hormone therapy, targeted therapy, chemotherapy, surgery, and radiation therapy. The NCI also noted that patients may join clinical trials for new treatment methods and medications.

Metastatic breast cancer treatment can depend on the subtype of the breast cancer and whether the person is premenopausal or postmenopausal. Menopause is the time in life when your period stops as part of aging.

Some examples of treatments include, per the NCI:

  • Hormone therapy: Hormones can cause certain cancers to grow, so this therapy involves removing or blocking these hormones. Medication, surgery, and radiation therapy can be used.
  • Chemotherapy: Medication can help stop the growth of cancer cells.
  • Radiation therapy: Providers use x-rays or other types of radiation to kill or prevent the growth of cancer cells.
  • Targeted therapy: This treatment attacks specific cancer cells and is typically less harmful than chemotherapy or radiation therapy.
  • Surgery: Cancer can be removed from specific organs, sometimes followed by radiation therapy.
  • Chemotherapy and immunotherapy: This combines chemotherapy with a treatment that uses the patient's immune system to fight the cancer.

Note that chemotherapy, hormone therapy, targeted therapy, and immunotherapy are all treatments that use systemic medications—they treat cancer throughout the body, according to Breastcancer.org. Surgery and radiation therapy are localized to the sites of the metastatic cancer.

Patients may also receive palliative care—special treatment or medical care for symptoms and discomfort of a serious illness such as cancer, per the National Institute on Aging. Palliative care providers are trained specifically to help patients manage side effects from their cancer treatment or other cancer-related issues.


A person can help reduce their risk of breast cancer through lifestyle changes, though there is no sure way to prevent the disease. Here are some things you can do to reduce your risk of breast cancer, per MedlinePlus:

  • Maintain a healthy weight
  • Reduce alcohol use
  • Exercise
  • Limit your exposure to estrogen

People who have a high genetic risk of breast cancer may also speak with their healthcare provider about taking specific medications or getting a mastectomy—surgery to remove part or all of the breast.

Regular screenings such as mammograms and the right treatment at an earlier stage of the breast cancer can help prevent the spread, but nothing can guarantee that the cancer doesn't metastasize, according to Breastcancer.org.

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