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Frequently Asked Questions about Brain Metastasis

What's a good, simple resource to help me understand the parts of the brain and their function?

Try reading "Parts of the Brain" from the American Brain Tumor Association, or take an "Interactive Tour of the Brain" from the National Brain Tumor Foundation.

If I have metastatic breast cancer, what is my risk of having a brain metastasis? Are some patients at higher risk? 

Breast cancer metastasizes (spreads) to the brain in about 15-20% of women with metastatic disease. However, some factors put patients at higher risk. Women who are under fifty years of age, who have HER2-positive tumors, estrogen receptor-negative tumors, and lung or liver metastases are somewhat more likely to be diagnosed with brain metastases. Studies indicate that mutations in the BRCA1 gene are also a risk factor. Women who have HER2 metastatic disease have a risk of brain metastases ranging from 25-40%.   

If I don’t have brain metastases now, should I have a scan?  

Standard of care does not currently call for routine screening for brain metastases in the absence of symptoms. Some doctors do recommend MRIs routinely for their metastatic patients considered at high risk for brain metastases—for example, those with HER2-positive tumors.  However, picking up brain metastases early, when they are easier to treat, has not yet been shown to extend life in research studies.  (For more, read what Dr. Andrew Seidman has to say about screening for brain mets.)  

Are single or multiple brain metastases more common?   

Fifty percent of the time a single metastasis appears in the brain.  For the other half of patients, multiple brain metastases occur.  Although some brain metastases occur as the first site of metastatic disease, most of the time, they occur later in the course of metastatic breast cancer (and called solitary brain metastases). Generalized swelling, as well as the location of metastases in the brain, determines what physical, mental, or sensory functions will be affected.

What kinds of treatments are available?  

Treatment for breast cancer brain metastases today consists of whole brain radiation, stereotactic radiosurgery (targeted high-dose radiation), and surgery. Chemotherapy has a limited though expanding role. Initial treatment decisions usually depend upon on size and number of metastases in the brain, and whether metastatic disease is present and under control outside the brain. (For details, see the Treatments section.) 

What is the blood-brain barrier?

The blood-brain barrier regulates which substances in the blood stream gain access to the brain and which do not.  It is comprised of tightly packed cells that line the small blood vessels that reach into the brain and spinal cord, forming a "wall" that prevents most bacteria, viruses and toxins in the blood stream from reaching the sensitive brain tissue.  These cells also have the ability to pump toxins trying to get into the brain back into the blood stream. 

Unfortunately, the blood-brain barrier also prevents most breast cancer treatments (and other drugs) from penetrating into the brain.  The smaller the molecules of a drug are, the easier it is for them to squeeze through the blood-brain barrier.  As they grow, brain metastases can disrupt the blood-brain barrier, allowing drugs to penetrate to a greater extend.

As women are living longer with well-controlled metastatic disease in other organs, developing new therapies that penetrate the blood brain barrier has become an important priority. Already a few new drug therapies have shown promise in treating breast cancer brain metastases. Also under study are ways to disrupt or penetrate the blood brain barrier so that treatments are able to reach the brain.