More common than primary brain tumors, which originate in the brain, brain metastases occur when cancerous cells break away from primary tumors in distant tissues or organs, then travel to the brain via the bloodstream or lymphatic system. While any type of cancer can potentially spread to the brain, the cancers most commonly associated with brain metastases initially develop in the colon, thyroid or skin (melanoma), or a kidney, lung or breast. In some cases, the site of the primary cancer cannot be determined. For instance, the primary site may be too small to cause symptoms or show up in tests.
Metastatic cancer is referred to by the name of the primary cancer. For example, when cancer spreads from a breast to the brain, the brain tumor is made up of breast cancer cells and the cancer is known as metastatic breast cancer, not brain cancer.
Why does cancer sometimes spread to the brain?
Rapidly dividing cancer cells are often capable of separating themselves from a primary tumor. If tumor cells enter the bloodstream or lymphatic system, the body’s immune system will usually attempt to destroy them. However, if the number of circulating tumor cells is very high, the immune system may become overwhelmed or tolerant of them. Instead of being destroyed, the traveling cancer cells may exit the bloodstream or lymphatic system in another part of the body, then invade a distant tissue or organ.
The growth rate of a metastatic tumor is unrelated to the growth rate of the primary tumor. For instance, because blood flows directly from the lungs to the brain, lung cancer can spread to the brain very quickly—sometimes so fast that a brain metastasis is detected before the primary lung cancer is diagnosed.
Primary cancers tend to spread to particular organs. Researchers believe these organ preferences may be caused by small attractant molecules (chemokines), which guide the tumor cells to the metastatic sites. Cancer cells may also adhere to certain organs due to the adherent molecules expressed by those organs.
"We now have treatment options that include medications, surgery and focused radiation treatment. Our highly coordinated team can help to guide patients as to which treatment or treatments are best for each situation."- Dr. Peter Forsyth, chair of the Neuro-Oncology Program
What are the symptoms of brain metastases?
Both primary brain tumors and brain metastases can cause similar symptoms, which can vary based on the location of the tumor within the brain. Some common symptoms include:
The brain does not have pain receptors, but a brain tumor can cause headaches in several ways. In addition to invading and destroying healthy tissues, a growing tumor may press on the brain and cause it to swell, increasing the pressure inside the skull (intracranial pressure), which cannot expand to accommodate it. Instead, the dura—a sensitive membrane that covers the brain and spinal cord—may become painfully stretched.
Additionally, a brain tumor can block the flow of cerebrospinal fluid, which coats and cushions the brain and spinal cord. As a result, the cerebrospinal fluid may build up in the brain and increase intracranial pressure. A brain tumor may also stretch blood vessels in the brain or release inflammatory proteins (cytokines), both of which could cause headaches.
Different regions of the brain control different functions, such as the ability to think, talk, feel, see, hear, remember, walk and more. Depending on its location, a brain tumor or its treatment may cause cognitive disturbances, such as short-term memory loss and behavioral changes, or motor problems, such as weakness on one side of the body or loss of balance.
Normally, the nerve cells in the brain communicate with each other through carefully controlled electrical signals. A brain tumor may suddenly disrupt these signals by causing a brief episode of abnormal electrical activity. The result is a partial or generalized seizure, which can cause changes in behavior, movements, feelings or levels of consciousness.
How are brain metastases diagnosed?
If a brain metastasis is suspected, the physician will ask the patient about any mental, emotional or physical changes he or she recently experienced. Next, the patient will undergo a physical examination and one or more imaging tests, such as magnetic resonance imaging (MRI), which can help the physician identify a brain tumor. If the imaging is inconclusive, the physician may order a biopsy to remove a small piece of the suspected tumor so that it can be tested. A brain biopsy may be performed surgically or with a needle guided by specialized navigation equipment.
What are the risk factors for brain metastases?
Studies show that appropriately one-third of patients with another type of cancer will develop brain metastases. The risk for metastatic brain tumors begins to increase after age 45 and is highest after age 65.
Are brain metastases treatable?
Metastatic brain tumors are often treatable and can be well controlled. To determine the optimal treatment approach, a neurosurgeon will consider multiple factors that are unique to the patient, including:
- The type and current status of the primary cancer
- The number and location of brain metastases
- The patient’s symptoms, general health and treatment preferences
Groundbreaking treatment options available at Moffitt Cancer Center
Moffitt Cancer Center is a well-established leader of brain cancer treatment, research and supportive care. We take a team approach that leverages the combined expertise of our neurosurgeons, medical oncologists, radiation oncologists, neuroradiologists and other experts who focus exclusively on brain tumors. In recognition of our extensive research and steadfast commitment to advancing brain cancer treatment, the National Cancer Institute has designated Moffitt as a Comprehensive Cancer Center, and we are the only such center based in Florida. Because we are a high-volume cancer center, our brain cancer treatment team has acquired an unparalleled level of experience in addressing even the most complex brain metastases.
Medically Reviewed by Peter Forsyth, MD, chair of the Neuro-Oncology Program.
If you would like to speak with a specialist in our Neuro-Oncology Program about our approach to treating brain metastases, contact Moffitt Cancer Center at 1-888-663-3488 or submit a new patient registration form online.