Brain Tumors Facts
What Are Brain Tumors?
Brain tumors are rare — less than 1 percent of the population is diagnosed with a malignant (cancerous) brain tumor during their lifetime. Cancers that begin in the brain – primary brain tumors – are uncommon, while those that travel to brain tissue from other organs – called metastatic tumors – are more frequently diagnosed.
In 2016, around 78,000 people in the United Stated will be diagnosed with a primary brain tumor — most of which will be benign (noncancerous) — and approximately 200,000 will be diagnosed with brain tumors that metastasized from other parts of the body. The most common cancers that metastasize to the brain include:
How Brain Cancer Develops
The brain is a three-pound mass of fatty tissue mainly composed of nerve cells — which convey messages from the brain and spinal cord to the rest of the body — and glial cells, which surround and support nerve cells. The brain controls basic functions like breathing and more complex ones like emotions and personality.
Other structures in and around the brain include the:
- Meninges, thin layers of tissue that surround the brain and spinal cord
- Ventricles, fluid-filled spaces in the center of the brain
- Cerebrum, the largest and most developed part of the brain that governs complex things like emotions, personality and judgment
- Cerebellum, located in the lower back part of the brain, and the seat of motor control
- Brain stem, located at the base of the brain and connected to the spinal cord, which controls involuntary functions like breathing and heart rate
Brain cancer develops when abnormal cells in the brain and spinal cord grow and divide in an uncontrolled way, interfering with normal brain functioning. There are more than 120 types of brain and central nervous system tumors and they are classified based on the origin of the cells and how aggressively they behave.
Types of Brain Cancer (Primary)
Primary brain tumors are broadly categorized based on where they develop. Some tumors develop within brain tissue while others develop nearby (but outside the brain), putting pressure on brain tissue. Different brain tumor types require different treatments. The main types of primary brain tumors include:
- Meningiomas are most often benign. They sprout not from brain tissue itself but from thin, protective layers of the brain called the meninges. Meningiomas tend to grow slowly and can become quite large before causing symptoms. Approximately one-third of brain tumors are meningiomas.
- Gliomas, another common type of brain tumor, arise from cells (called glia) in the brain that form a protective and supportive “glue” around neurons. Most malignant brain tumors are gliomas. Several tumor types arise from glial cells including:
- Astrocytomas develop from star-shaped brain cells called astrocytes and are the most common form of glioma. Aggressive astrocytomas, called glioblastoma multiforme, are the fastest-growing type of malignant brain tumor. Astrocytomas tend to spread tentacle-like through normal brain tissue, making them difficult to remove surgically. Astrocytomas are rated based on how fast they grow — from high grade (fast-growing) to low grade (slow-growing).
- Oligodendrocytomas develop from cells called oligodendrocytes. They are more likely to grow slowly but can become more aggressive over time. Like astrocytomas, oligodendrocytomas tend to infiltrate normal brain tissue, making this type of tumor difficult to remove surgically.
- Ependymomas grow from ependymal cells, which are found in the ventricles. Unlike astrocytomas and oligodendrocytomas, this type of tumor usually does not grow into normal brain tissue, making it more likely to be removed with surgery. Since this type of brain tumor affects the ventricles, it can block the flow of cerebrospinal fluid and cause a condition called hydrocephalus.
- Mixed gliomas are tumors made up of two or more types of glioma cells, including astrocytomas, oligodendrocytomas and ependymomas. Mixed gliomas usually are treated based on the behavior of the most aggressive cells in the tumor.
Other Brain Tumor Types
- Pituitary tumors are usually benign tumors that start in the pituitary gland and represent around 15 percent of all primary brain tumors.
- Chordomas are rare, slow-growing tumors that form along the spine and sometimes metastasize to other parts of the body.
- Schwannomas, also called acoustic neuromas, neurilemmomas and vestibular schwannomas, develop from Schwann cells — which form the protective coating around nerve fibers. They are usually slow-growing and benign.
- Gangliogliomas are extremely rare tumors, more common among children and young adults, that involve neurons and glial cells.
- Craniopharyngiomas grow near the base of the brain, and because they develop in close proximity to the pituitary region and optic nerves, may affect hormones and vision when they grow.
- Lymphomas are aggressive tumors that start in immune system cells called lymphocytes. Lymphomas that begin in the brain are more common among people who are immunocompromised, such as those with HIV.
- Medulloblastomas are fast-growing tumors that develop from neuroectodermal cells in the cerebellum.
Brain Tumor Grading
While other cancer types are staged based on how quickly the disease progresses and how far from the primary site they spread, brain and spinal cancers almost never travel to other body parts. Brain tumors are graded based on their growth rate and how the cells appear under a microscope:
- Grade I is benign tumor tissue that grows slowly and closely resemble normal brain cells.
- Grade II is malignant tissue that look less normal than Grade I cells.
- Grade III describes fast-growing (anaplastic) malignant cells that look very different from Grade I cells.
- Grade IV are fast-growing malignant cells that look the most abnormal.
Lower grade brain tumors grow more slowly than high-grade, but may develop into high-grade tumors over time.
What Increases Your Risk of Brain Cancer?
Things that put you at higher risk for getting brain cancer are called risk factors. There are very few known causes of primary brain tumors, although age, certain genetic syndromes and radiation exposure play a role in some cases. Factors that increase the risk of a brain tumor include:
- Radiation exposure from high-dose radiation therapy and other sources.
- Age; people tend to be diagnosed either in childhood or as older adults.
- Immune system disorders increase the risk that a person will develop lymphomas affecting the brain and spinal cord.
Family History and Genetic Influences
Having multiple family members with brain tumors, in rare cases, can dictate whether a person develops a brain tumor. Fewer than 5 percent of glioma patients have a family history of brain tumor.
- Tuberous sclerosis increases the risk of certain low-grade astrocytomas and benign tumors of the brain, heart, skin and other organs.
- Von Hippel-Lindau syndrome increases the risk of developing benign or malignant tumors in different parts of the brain and spinal cord; and other parts of the body including the pancreas, kidney, adrenal gland and inner ear.
- Neurofibromatosis type 1 and 2 are nerve tumors of the skin, brain or spinal cord. Problems with the NF1 gene are much more likely to be implicated as a cause of brain tumors than changes to NF2.
- Li Fraumeni cancer syndrome is caused by changes to a gene called TP53 and is associated with a higher risk of developing gliomas and other types of cancer including sarcomas, leukemia and breast cancer.
- Other rare syndromes that increase the risk of brain tumors include Gorlin syndrome, Turcot syndrome and Cowden syndrome.
Brain Cancer Symptoms
Symptoms of brain cancer depend on which parts of the brain are involved and how quickly the tumor is growing. For slower-growing tumors, symptoms may come on gradually, while for more aggressive tumors they can come on quickly. Because there tend to be no early symptoms, brain tumors may be advanced by the time they are discovered.
Both benign and malignant tumors cause similar symptoms, including:
- Nausea and vomiting
- Weakness or numbness in areas such as face, arms or legs
- Balance and coordination problems
- Behavior and personality changes
- Memory problems
- Blurry vision
- Speech or hearing problems
- Other neurologic impairment
Headache is one of the most common symptoms of brain cancer — it may be caused by a tumor pressing on the brain, swelling or bleeding — and tends to be worse in the morning.
Other medical conditions share these symptoms. If you have any of these conditions, you may need further consultation to rule out brain cancer.