Breast cancer is the most common type of cancer in women in the United States. When cancer metastasizes, it spreads to a distant part of the body from where it originated. Metastatic cancer is also called stage 4 cancer.

According to the American Cancer Society, breast cancer makes up about 30% of all new cancers diagnosed in women each year.

The brain is one of the locations where breast cancer can commonly metastasize. Keep reading to learn more about brain metastasis, its symptoms, and how it’s diagnosed and treated.

Brain metastasis happens when cancer that starts in one area, such as the breast, spreads to the brain. The brain is one of the common sites of breast cancer metastasis. Other sites include the bones, lungs, and liver.

A 2017 study looked at 4,932 people with metastatic breast cancer. Within this population, 8.8% had a brain metastasis.

For many people, healthcare professionals detect metastases in other common metastatic sites before finding them in the brain. However, the advocacy organization Breastcancer.org says about 17% of people with metastatic breast cancer have the brain as their only site of metastasis.

The symptoms of brain metastasis depend on which part of the brain is affected and may include:

Other more general symptoms that breast cancer has metastasized include:

Metastasis happens when cancer cells break away from the original tumor site. These cells use the circulatory or lymphatic system to travel to a more distant part of the body, such as the brain, and establish a new tumor.

It’s not possible to predict with certainty whether or not a person will develop brain metastasis. However, some factors can increase a person’s risk.

Risk factors for brain metastasis

According to a 2020 review, the risk factors for brain metastasis are similar to the general risk factors for metastatic breast cancer. These include having:

If you’ve received a breast cancer diagnosis, remember that having any of the above risk factors doesn’t mean that you’ll certainly develop brain metastasis. It means you’re at an elevated risk compared with others without risk factors.

If your symptoms suggest the presence of brain metastasis, your doctor can use a variety of tests to make a diagnosis.

Initially, a doctor will order blood tests to understand your overall health and the function of various organs. These can include:

Your doctor can use a head MRI to confirm the diagnosis of brain metastasis. They’ll typically give a contrast solution via an intravenous (IV) line to help make the MRI images clearer.

The treatment that healthcare professionals recommend for brain metastasis can depend on several factors, including:

  • the number of different spots of metastases present in the brain
  • the location of the metastases in the brain
  • the HER2-positive and ER-positive status of your cancer
  • whether your cancer has also metastasized to other areas of the body
  • whether certain genetic changes are present in your cancer
  • your age and overall health
  • your personal preferences

There are several potential treatment options for brain metastasis. Doctors generally divide these treatments into two categories: local and systemic.

A healthcare professional will specifically direct local treatments at the site of the metastatic tumor. Systemic treatments work on the entire body. Depending on your individual situation, doctors may use a combination of local and systemic treatments.

Local treatments

In some cases, a doctor can remove the brain metastases surgically. They usually recommend this for people in good overall health with a few brain metastases that are easy to access. The healthcare team often follows this with radiation therapy.

Stereotactic radiosurgery is another potential option for people with few metastases. It directs a single, strong dose of radiation at the affected area. The radiation aims precisely at the tumor and not the surrounding tissue.

If many brain metastases are present, treatment may involve whole-brain radiation over several sessions instead of local treatments.

Systemic treatments

Hormone therapy blocks the action of hormones like estrogen and progesterone on cancer cells that are ER-positive. This can decrease further growth and division of cancer cells. Doctors may recommend it in combination with targeted therapy.

Targeted therapy works by interfering with the activity of specific proteins on or inside cancer cells. Examples of targeted proteins are HER2 and cyclin-dependent kinases (CDK), which are proteins involved with cell growth.

Immunotherapy helps your immune system to fight cancer. A type of drug called an immune checkpoint inhibitor may be helpful for triple-negative breast cancer. This type of breast cancer is harder to treat with targeted therapy, and doctors cannot treat it with hormone therapy.

Other treatments

People with brain metastases can often have swelling around the brain. Doctors may prescribe steroids like dexamethasone to help alleviate this.

Seizures are also a potential symptom of brain metastasis. If you’re having seizures, your doctor will prescribe antiseizure medications to help prevent them.

According to the National Cancer Institute (NCI), the 5-year survival rate for metastatic breast cancer is 29%. This means that, compared with people without this type of cancer, 29% of people with metastatic breast cancer are alive after 5 years.

The outlook for brain metastases itself is generally less favorable, but several factors can influence it, such as:

  • the HER2 and HR status of your cancer, with triple-negative breast cancer having the least favorable outlook
  • the number of metastases present in the brain
  • whether your cancer has also metastasized to other areas of the body
  • the type of treatments you receive and your response to them
  • your age and overall health

A 2019 study looked at 4,118 people with breast cancer and brain metastases. Over a 30-month follow-up period, the median overall survival after diagnosis of brain metastases was 7.9 months.

A 2020 study noted that survival for brain metastases has improved overall. However, for metastatic breast cancer in the brain, survival varied between 3 and 36 months.

When discussing survival rates, numbers relate to large studies of people diagnosed several years ago. They don’t reflect individual situations or recent advances in diagnosis and treatment.

Consider a clinical trial

Doctors and scientists continue researching new cancer treatment approaches, including brain metastases. They test these new approaches in clinical trials.

If you’re interested in trying an experimental treatment option, talk with your oncology care team about clinical trials for which you may be eligible. You can also find a searchable database of NCI-supported clinical trials here.

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Here are some frequently asked questions about when breast cancer metastasizes to the brain.

How long can you live when breast cancer spreads to the brain?

For metastatic breast cancer that has spread to the brain, survival varies between 3 and 36 months.

What is the life expectancy of a brain metastasis patient?

According to a 5-year study, patients’ overall survival after their brain metastasis diagnosis was around 6 months. However, recent advances in diagnosis and treatment mean life expectancy continues to change.

What is the outlook when cancer spreads to the brain?

The outlook for brain metastases is generally less favorable, but several factors affect this, and no two cancers are the same. Metastatic brain cancer can be terminal, and most people may live for less than a year after diagnosis.

What are the final stages of brain metastases?

End-of-stage brain metastasis symptoms include less need for food and drink, withdrawal, and changes in breathing.

The brain is a common site for breast cancer to metastasize or spread. Brain metastasis can lead to symptoms like headache, weakness in your limbs, and seizures.

Imaging with a head MRI is the main way doctors diagnose brain metastases. Treatment approaches may be local, systemic, or a combination of both. Your treatment plan will depend on your particular situation.

While the outlook for breast cancer that metastasizes to the brain is generally poor, your doctor can help to give you a better idea of your treatment plan. Additionally, research into new advances in treatment is ongoing.