Breast cancer is the most common type of cancer in women in the United States. According to the American Cancer Society (ACS), it makes up about 30 percent of all new cancers diagnosed in women each year.

All cancers, including breast cancer, can metastasize. This is when cancer spreads to a more distant part of the body from where it originated. Metastatic cancer is also called stage 4 cancer.

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

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

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

For many people, metastases have already been detected in another of the common metastatic sites before they are found in the brain. However, says that about 17 percent of people with metastatic breast cancer have the brain as their only site of metastasis.

The symptoms of brain metastasis can 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, blood tests will be ordered to get an idea of 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. This will typically be done with a contrast solution that’s given via an intravenous (IV) line. Using a contrast solution can help to make the images from the MRI clearer.

The treatment that’s recommended for brain metastasis can depend on a few factors, including:

  • how many metastases are present in the brain
  • where in the brain the metastases are located
  • the HER2-positive and ER-positive status of your cancer
  • whether your cancer has also metastasized to other areas of the body
  • if 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.

Local treatments are specifically directed at the site of the metastatic tumor. Systemic treatments work on the entire body. Depending on your individual situation, a combination of local and systemic treatments may be used.

Local treatments

In some cases, brain metastases can be removed surgically. This is typically recommended for people in good overall health with a small number of brain metastases that can be easily accessed. It’s often followed by radiation therapy.

Stereotactic radiosurgery is another potential option for people with a small number of metastases. It directs a single, strong dose of radiation at the affected area. The radiation is aimed very precisely in order to affect the tumor and not surrounding tissues.

Whole-brain radiation is when radiation is given to the whole brain, typically over several sessions. This approach may be used when many brain metastases are present and other local treatments aren’t recommended.

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. It’s often used in combination with targeted therapy.

Targeted therapy works by interfering with the activity of specific proteins that are on or inside of cancer cells. Examples of proteins that are targeted 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 cannot be treated with hormone therapy.

Other treatments

People with brain metastases can often have swelling around the brain. To help alleviate this, steroids such as dexamethasone may be used.

Seizures are also a potential symptom of a 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 percent. This means that, compared with people without this type of cancer, 29 percent of people with metastatic breast cancer are alive after 5 years.

The outlook for brain metastases itself is generally poor, but can be influenced by several factors, such as:

  • the HER2 and HR status of your cancer, with triple-negative breast cancer having the poorest outlook
  • how many metastases are present in the brain
  • whether your cancer has also metastasized to other areas of the body
  • the type of treatments that have been used 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, median overall survival after diagnosis of brain metastases was 7.9 months.

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

When we discuss survival rates, know that these numbers are based on studies of large numbers of people who were 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 to research new approaches for treating cancer, including brain metastases. These new approaches are tested in clinical trials.

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

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

Imaging with a head MRI is the main way that 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’s metastasized to the brain is generally poor, your doctor can help to give you a better idea of your individual outlook. Additionally, new advances in treatment are being researched all the time.