Brain Tumor: Introduction

Approved by the Cancer.Net Editorial Board, 03/2023

ON THIS PAGE: You will find some basic information about this disease and the parts of the body it may affect. This is the first page of Cancer.Net’s Guide to Brain Tumors. Use the menu to see other pages. Think of that menu as a roadmap for this entire guide.

The possibility of being diagnosed with a brain tumor can be a shocking and life-changing event. If your doctor suspects a brain tumor, it is important to seek out doctors who specialize in diagnosing and treating brain tumors. The brain is a complex and vital organ, and treatment often causes life-long changes. Research about brain tumor treatment is ongoing, so it is important to get updated medical information about treatment options about the specific type of brain tumor and to get specialists' opinions about your treatment plan.

About the brain and central nervous system

The brain and spinal column make up the central nervous system (CNS), where all vital functions are controlled. These functions include thought, speech, and body movements. This means that when a tumor grows in the CNS, it can affect a person's thought processes or the way they talk or move.

Anatomy of the brain

The brain is made up of 3 main parts: the cerebrum, the cerebellum, and the brain stem. The meninges, which surround the brain, are also considered part of the brain.

  • The cerebrum.This is the largest part of the brain. It contains 2 cerebral hemispheres on either side of the brain that each control the opposite side of the body. It is divided into 4 lobes where specific functions occur:

    • The frontal lobe controls reasoning, emotions, problem-solving, expressive speech, and movement.

    • The parietal lobe controls the sensations of touch, such as pressure, pain, and temperature. It also controls parts of speech, visual-spatial orientation, and calculation.

    • The temporal lobe controls memory, special senses such as hearing, and the ability to understand spoken or written words.

    • The occipital lobe controls vision.

  • The cerebellum. The cerebellum is located at the back part of the brain below the cerebrum. It is responsible for coordination and balance, and it controls functions on the same side of the body.

  • The brain stem. This is the portion of the brain that connects to the spinal cord and the cerebellum. It controls involuntary functions essential for life, such as the beating of the heart and breathing. Messages for the functions controlled by the cerebrum and cerebellum travel through the brain stem to the body.

  • The meninges. These are the membranes that surround and protect the brain and spinal cord. There are 3 meningeal layers, called the dura mater, arachnoid, and pia mater. The cerebrospinal fluid (CSF) is made near the center of the brain, in the lateral ventricles. CSF circulates around the brain and spinal cord between the arachnoid and pia layers.

The image is two drawings showing different parts of a person’s brain. The largest part of the brain, the cerebrum, is made up of four lobes: the frontal lobe at the front of the skull, the parietal lobe at the upper rear of the skull, above the occipital lobe, which is at the back of the skull, and the temporal lobe, which is located under the frontal and parietal lobes on both sides of the cerebrum. The cerebellum is located under the occipital and temporal lobes at the rear of the skull. The brain stem includes the pons and the medulla oblongata, which connects to the spinal cord. Copyright 2004 American Society of Clinical Oncology. Robert Morreale/Visual Explanations, LLC.

About primary brain tumors

A primary brain tumor is a tumor that starts in the brain. A primary brain tumor is often described as either "low grade" or "high grade." A low-grade tumor generally grows slowly, but it can turn into a high-grade tumor. A high-grade tumor is more likely to grow faster.

In adults, a secondary brain tumor, also called a brain metastasis, is much more common than a primary brain tumor.

About secondary brain tumors

A secondary brain tumor, or brain metastasis, is a cancerous tumor that started in another part of the body, such as the breast, lung, or colon, and then spread to the brain. A secondary brain tumor may also be called metastatic cancer. For instance, lung cancer that has spread to the brain may be called metastatic lung cancer.

If cancer spreads to the meninges and CSF, it is called leptomeningeal metastases or neoplastic meningitis. This condition occurs more commonly in people with leukemia, lymphoma, melanoma, breast cancer, or lung cancer.

The rest of this guide mainly covers primary brain tumors in adults, while providing some information on brain metastases. To learn more detailed information about cancer that started elsewhere in the body and spread to the brain, read about that specific type of cancer. Learn about brain tumors in children in a different guide on this same website.

Types of primary brain tumors in adults

There are many types of primary brain tumors. Some cannot be assigned an exact type because the tumor’s location makes it too difficult to remove for full testing.

Descriptions of more common brain tumor types in adults are described below, divided into glioma and non-glioma tumor types.


As a group, gliomas are one of the most common types of brain tumors. While the exact origin of gliomas is still unknown, they are thought to grow from glial cells or glial precursor cells. A glial cell is a type of supportive cell in the brain. The main types of supportive cells in the brain include astrocytes, oligodendrocytes, and ependymal cells. Gliomas may be considered astrocytoma, oligodendroglioma, or ependymoma. Gliomas are assigned a grade, which is an indication of how aggressive a tumor is likely to be. A higher grade is usually more aggressive and more likely to grow quickly. However, current research is helping doctors move toward using tumor genetics to better classify gliomas. This is discussed elsewhere in this guide. Unlike most tumors that start outside of the brain and CNS, most primary brain tumors like glioma are not assigned a "stage." For tumors that do not begin in the brain, a higher cancer "stage" number usually describes whether the primary tumor has spread to other parts of the body, and this information influences which treatments are selected. Primary brain tumors, like gliomas, only rarely spread outside of the brain. Thus, they do not need to be staged to help the clinical team decide on the appropriate treatments.

Currently, the types of gliomas include:

  • Astrocytoma. Astrocytoma is the most common type of glioma. Astrocytoma cells look like glial cells called astrocytes that are found in the cerebrum or cerebellum. Historically, there have been 4 grades of astrocytoma, which are described below.

    • Grade 1 or pilocytic astrocytoma is a slow-growing tumor that is most often benign and rarely spreads into nearby tissue. Benign means the tumor can grow but does not spread to other parts of the body.

    • Grade 2 astrocytoma is a slow-growing malignant tumor that can often spread into nearby tissue and can become a higher grade. Malignant means it is cancerous and can spread to other parts of the body.

    • Grade 3 or anaplastic astrocytoma is a malignant tumor that can quickly grow and spread to nearby tissues.

    • Grade 4 or glioblastoma is a very aggressive form of astrocytoma.

    A new international classification system for primary brain tumors was unveiled by the World Health Organization (WHO) in 2021. This system divides astrocytomas and other types of brain tumors into many subgroups depending largely on their genetic makeup and the presence or absence of certain important changes in the tumor's specific genes. The treatment team will use information from an analysis of each tumor sample to precisely classify each tumor using the new guidelines. (Learn more about biomarker testing of the tumor in the Diagnosis section.) Key changes for the most common types of astrocytomas include:

    • Adult diffuse astrocytomas have now been grouped based on whether there is a mutation in the isocitrate dehydrogenase (IDH) gene. There are 2 groups: 1) astrocytoma, IDH mutant, and 2) glioblastoma, IDH wild-type. "Wild-type" means that the gene is found in its natural, unmutated form.

    • Astrocytoma, IDH mutant, can be a grade 2, grade 3, or grade 4 tumor, based on whether there are other genetic and tumor features, including a high rate of cell division (called the mitotic index) and alterations in the CDKN2A/B genes. These were previously called IDH-mutant or secondary glioblastomas.

    • Glioblastoma is now only used to describe IDH wild-type tumors that also have 1 or more of the following features: loss of chromosome 10, gain of chromosome 7, TERT promoter mutation, and increased number of copies of the EGFR gene. Unlike the previous classification system, glioblastomas are do not also have to show signs of cell death and excessive growth of blood vessels.

  • Oligodendroglioma. Oligodendroglioma is a tumor whose cells look like glial cells called oligodendrocytes. These cells are responsible for making myelin. Myelin surrounds the nerves and is rich in protein and fatty substances called lipids. Under the 2021 WHO guidelines, these tumors must have an IDH mutation and contain a chromosome 1p and 19q codeletion. They are categorized as either grade 2 oligodendroglioma, which is considered low grade, or grade 3 oligodendroglioma, which is considered a high-grade tumor with anaplastic features.

  • Ependymoma. Ependymoma commonly begins in the passageways in the brain where CSF is made and stored. In adults, they occur more often in the spine and can also be of the myxopapillary subtype. Learn about ependymoma in children.

  • Diffuse midline glioma. A diffuse midline glioma begins in the glial cells in the brain stem, spinal cord, and other midline structures within the CNS. Learn about brain stem glioma in children.

Non-glioma tumors

Non-glioma tumors are tumors that arise from cells in the brain that are not glial cells. Types of non-glioma tumors include:

  • Meningioma. Meningioma is the most common primary brain tumor. It begins in the meninges and is most often noncancerous. Meningioma can cause serious symptoms if it grows and presses on the brain or spinal cord or grows into the brain tissue. Learn more about meningioma.

  • Pineal gland and pituitary gland tumors. These are tumors that start in the pineal gland and pituitary gland.

  • Primary CNS lymphoma. This is a form of lymphoma. Lymphoma is a cancer that begins in the lymphatic system. Primary CNS lymphoma starts in the brain and can spread to the spinal fluid and eyes.

  • Medulloblastoma. Medulloblastoma is thought to start from a specific type of cell in the cerebellum. These cells are called cerebellar granule progenitor cells. It is most common in children and is usually cancerous, often spreading throughout the CNS. Learn about medulloblastoma in children.

  • Craniopharyngioma. Craniopharyngioma is a benign tumor that begins near the pituitary gland located near the base of the brain. These tumors are uncommon. Learn about craniopharyngioma in children.

  • Schwannoma. Schwannoma is a rare tumor that begins in the nerve sheath, or the lining of the nerves. It may often occur in the vestibular nerve, which is a nerve in the inner ear that helps control balance. It is typically noncancerous.

For a complete list of all types of brain tumors and how often they are diagnosed, the website of the Central Brain Tumor Registry of the United States offers this information in its reports. (Please note that this link takes you to another organization's website.)

Looking for More of an Introduction?

If you would like more of an introduction, explore these related items. Please note that these links will take you to other sections on Cancer.Net:

The next section in this guide is Medical Illustrations. It offers drawings of body parts often affected by a brain tumor. Use the menu to choose a different section to read in this guide.