Brain tumors are named based on where they start, what type of cell they grow from, and how fast they grow. There isn’t one single name for a brain tumor. Instead, there are over 100 recognized types, each with its own name. The broadest distinction is between primary brain tumors, which originate in the brain itself, and secondary brain tumors (also called brain metastases), which are cancers that spread to the brain from elsewhere in the body.
Primary vs. Secondary Brain Tumors
A primary brain tumor is any tumor that starts in the brain or its surrounding tissues. These can be cancerous (malignant) or noncancerous (benign). They’re named after the specific cell type they grow from, such as glial cells, meningeal cells, or nerve cells.
A secondary brain tumor, or brain metastasis, is cancer that traveled to the brain from another organ through the bloodstream. These tumors keep the name of their original cancer. So if lung cancer spreads to the brain, the tumor in the brain is still made of lung cancer cells and is treated as lung cancer, not as a “brain tumor” in the traditional sense. The cancers most likely to spread to the brain are lung cancer, breast cancer, colon cancer, kidney cancer, and melanoma.
Gliomas: The Most Common Category
About 33 percent of all brain tumors are gliomas, making this the most common category at all ages. Gliomas grow from glial cells, the supportive cells that surround and protect neurons. Within that broad group, tumors get more specific names based on exactly which type of glial cell is involved.
Astrocytomas develop from star-shaped glial cells called astrocytes. They account for nearly half of all primary brain tumors and range from slow-growing, low-grade forms to highly aggressive ones. The most aggressive version is called glioblastoma (sometimes written as glioblastoma multiforme), which is the most malignant of all brain tumors.
Oligodendrogliomas grow from a different type of glial cell. Under the current classification system, a tumor is only called an oligodendroglioma if it has two specific molecular features: a mutation in a gene called IDH and a chromosomal change known as 1p/19q co-deletion. This is one example of how modern brain tumor names now depend on molecular testing, not just what the cells look like under a microscope.
Ependymomas arise from cells lining the fluid-filled cavities (ventricles) inside the brain. They’re more common in children and can occur in both the brain and spinal cord.
Meningiomas: The Most Common Benign Type
Meningiomas grow in the meninges, the protective layers of tissue surrounding the brain and spinal cord. They are the most common benign brain tumor in adults. Most meningiomas grow slowly and may not cause symptoms for years. Although the majority are benign, a small number are faster-growing or, rarely, malignant.
Other Named Types
Beyond gliomas and meningiomas, several other brain tumors have distinct names based on where they form or what cells they involve:
- Pituitary adenomas grow in the pituitary gland at the base of the brain. Most are benign and may affect hormone levels.
- Acoustic neuromas (also called vestibular schwannomas) develop on the nerve connecting the inner ear to the brain. They’re benign but can cause hearing loss and balance problems as they grow.
- Craniopharyngiomas form near the pituitary gland and are more common in children.
- Gangliogliomas are mixed tumors containing both nerve cells and glial cells. They tend to be low-grade and are more common in young people.
Brain Tumors in Children
Children develop some brain tumor types that are rare or nonexistent in adults. The most common pediatric brain tumors, in order of frequency, are medulloblastoma, juvenile pilocytic astrocytoma, ependymoma, diffuse intrinsic pontine glioma (DIPG), and atypical teratoid rhabdoid tumor (ATRT).
Medulloblastoma is an aggressive tumor made of small, rapidly dividing cells that forms in the back of the brain (the cerebellum). It’s always classified as high-grade. Juvenile pilocytic astrocytoma, by contrast, is a slow-growing glioma that is one of the most treatable childhood brain tumors. DIPG grows in the brainstem and is one of the most difficult pediatric brain tumors to treat because of its location.
How Brain Tumors Are Graded
In addition to their specific name, every brain tumor receives a grade from 1 to 4 under the World Health Organization (WHO) system. This grade reflects how aggressive the tumor is.
- Grade 1 tumors are slow-growing and least aggressive. Pilocytic astrocytomas and subependymomas fall here.
- Grade 2 tumors grow slowly but can recur or progress over time.
- Grade 3 tumors are actively growing and have features that suggest they could become more aggressive.
- Grade 4 tumors are the most aggressive. Glioblastoma, medulloblastoma, and diffuse midline glioma are all grade 4, regardless of how they look under a microscope.
The grade matters because it shapes the treatment approach and gives a general sense of prognosis. Some tumors, like diffuse midline glioma, are automatically classified as grade 4 based purely on their molecular profile, even if the tissue doesn’t look highly abnormal under a microscope.
Why Naming Has Gotten More Specific
Brain tumor names have changed significantly in recent years. The 2021 WHO classification system now requires molecular testing alongside traditional microscope analysis to classify many tumor types. Two tumors that look identical under a microscope may receive completely different names, grades, and treatment plans based on their genetic markers.
For diffuse gliomas in particular, testing for IDH gene mutations and 1p/19q co-deletion is now required for accurate classification. A tumor with an IDH mutation and 1p/19q co-deletion is called an oligodendroglioma. The same-looking tumor without those markers may be classified as an astrocytoma or glioblastoma. This molecular approach means the name your doctor gives a brain tumor carries more precise information about how it will behave and respond to treatment than older naming systems could provide.