General · EdgepediaSeptember 17, 20268 min read

Brain tumor

A brain tumor is an abnormal growth of cells in the brain or the rest of the central nervous system (CNS), which includes the brain and spinal cord. Tumors that begin in the brain are called primary brain tumors; tumors that start elsewhere in the body and spread to the brain are called metastatic brain tumors (brain metastases), and these are more common than primary brain tumors.¹ Both benign (non-cancerous) and malignant (cancerous) brain tumors can cause symptoms and require treatment, because any growth that presses on brain tissue can stop that part of the brain from working properly.¹

Key fact	Detail
Primary vs metastatic	Metastatic brain tumors are more common than primary brain tumors; up to half of brain metastases come from lung cancer¹
Benign share	Approximately 74% of all brain tumors are benign; meningioma is the most common non-malignant primary brain tumor²
Most common malignant type	Glioblastoma, accounting for 52.2% of all malignant primary brain tumors²
US incidence	6.2 new cases of malignant brain and other CNS tumors per 100,000 people per year (SEER, 2017 to 2021); about 24,740 malignant brain or spinal cord tumors estimated for 2026³^•⁴^•¹⁰
Global burden	Approximately 321,476 new cases and 248,305 deaths from brain and other CNS tumors worldwide in 2022³
Survival	5-year relative survival for glioblastoma is 28% at ages 15 to 39 and 6% at age 40 and older; for meningioma, 97% and 88%⁵
Staging	There is no standard staging system for adult brain and spinal cord tumors; diagnosis rests on tumor type, grade, location, and molecular features instead¹

Primary and metastatic tumors

Primary brain tumors begin in the brain or spinal cord and are named for the cell type they form in and where they first arise. They may spread within the brain or to the spine, but they rarely spread to other parts of the body.¹ Brain tumors account for 85% to 90% of all primary CNS tumors.³

Metastatic brain tumors arise when cancer from another organ spreads to the brain. Common sources include lung cancer, breast cancer, kidney cancer, and melanoma; up to half of metastatic brain tumors originate from lung cancer.¹ Cancer can also spread to the leptomeninges, the two innermost membranes covering the brain and spinal cord, a condition called leptomeningeal carcinomatosis.¹ A brain lesion in a patient with a previous cancer should not be assumed to be a metastasis, because that assumption could lead to overlooking appropriate treatment of a curable tumor.³

Types of primary brain tumors

Tumors are classified by the cell of origin. Glial tumors (gliomas) arise from glial cells, the supporting cells of the nervous system:¹

Astrocytic tumors begin in star-shaped astrocytes and range from pilocytic astrocytoma (grade I, slow-growing) through diffuse astrocytoma (grade II) and anaplastic astrocytoma (grade III) to glioblastoma (grade IV), which grows and spreads very quickly.¹
Oligodendroglial tumors begin in oligodendrocytes and include oligodendroglioma (grade II) and anaplastic oligodendroglioma (grade III).¹
Ependymal tumors begin in cells lining the fluid-filled spaces of the brain and spinal cord.¹

Non-glial types include meningiomas, which form in the meninges, the thin layers of tissue covering the brain and spinal cord, and are most common in adults; medulloblastomas, embryonal tumors most common in children or young adults; pineal parenchymal tumors; germ cell tumors; and craniopharyngioma, a rare grade I tumor that usually forms just above the pituitary gland.¹

WHO grading and classification

The World Health Organization (WHO) grades CNS tumors on a four-point malignancy scale based on histological features. Grade I tumors have low proliferative potential, are often discrete, and may be cured by surgical resection alone. Grade II tumors grow slowly but can invade nearby tissue and recur, and some progress to higher grade. Grade III cells look very different from normal cells and grow more quickly. Grade IV tumors grow and spread very quickly, may contain areas of dead cells, and usually cannot be completely removed by surgery.¹^•³ A TNM-based staging system was abandoned for CNS tumors because tumor size matters less than histology and location, the brain and spinal cord have no lymphatics so nodal status does not apply, and metastatic spread outside the CNS rarely develops.³

Molecular era. The international WHO classification of tumors was initiated through a resolution of the WHO Executive Board in 1956 and endorsed by the World Health Assembly in 1957; the first edition for the nervous system, edited by Klaus J. Zülch, director of the Max-Planck Institute for Brain Research in Cologne, was published in 1979.⁶ The 2016 edition was a conceptual advance: for the first time it used molecular parameters in addition to histology to define tumor entities, restructuring the diffuse gliomas and medulloblastomas and introducing entities such as glioblastoma, IDH-wildtype; glioblastoma, IDH-mutant; diffuse midline glioma, H3 K27M-mutant; and RELA fusion-positive ependymoma. It also added brain invasion as a criterion for atypical meningioma.⁷ Advances in molecular biology prompted a new classification in 2021, only five years after the prior iteration.⁸

Molecular features also shape prognosis. Tumors with a mutation in the IDH1 or IDH2 gene (IDH-mutant tumors) tend to grow more slowly and have a better outlook than tumors without these mutations.⁹

Symptoms and diagnosis

Signs and symptoms depend on where the tumor forms, what the affected part of the brain controls, and the tumor's size. Possible symptoms include morning headache or headache that goes away after vomiting, seizures, vision, hearing, and speech problems, frequent nausea and vomiting, changes in personality, mood, ability to focus, or behavior, loss of balance and trouble walking, weakness, and unusual sleepiness.¹

Diagnosis combines a neurological exam, imaging, and tissue sampling. MRI with gadolinium, a contrast agent that collects around cancer cells so they appear brighter, is often used, along with CT scanning; magnetic resonance spectroscopy can help characterize tumors by their chemical make-up, and PET scans can help distinguish a primary tumor from a metastasis.¹ When imaging suggests a tumor, a biopsy is usually performed, either as a stereotactic biopsy guided by 3-D scanning for tumors deep in the brain or as an open biopsy during a craniotomy. A pathologist determines the tumor type and grade, and tests on the tissue may include immunohistochemistry, cytogenetic analysis, and gene testing.¹ For some tumors in locations where biopsy or surgery cannot be done safely, diagnosis and treatment are based on imaging and other procedures.¹

Treatment

Treatment options for primary CNS tumors include surgery, radiation therapy, chemotherapy, active surveillance, and supportive therapy.³ For most tumor types in most locations, complete or near-complete surgical removal is attempted while preserving neurological function; removing tumor tissue also decreases pressure on nearby brain.¹^•³ Deep-seated tumors such as pontine gliomas are an exception and are treated without initial surgery about 50% of the time.³ Active surveillance, watching closely without treatment until tests show progression, may be used for very slow-growing tumors that cause no symptoms.¹

Radiation therapy uses high-energy x-rays or other radiation to kill cancer cells or keep them from growing. Intensity-modulated radiation therapy (IMRT) aims thin beams of different intensities at the tumor from many angles, and stereotactic radiosurgery uses a rigid head frame to deliver a single large dose precisely to the tumor without surgery.¹ Chemotherapy drugs used in adults include temozolomide, carmustine, lomustine, belzutifan, and eflornithine; some drugs cannot cross the blood-brain barrier, and a dissolvable wafer can deliver chemotherapy directly to the tumor site after surgical removal.¹ For glioblastoma, combined-modality therapy with resection, radiation, and chemotherapy is standard.³

Treatment of one to four brain metastases may include whole-brain radiation therapy with or without surgery or stereotactic radiosurgery, stereotactic radiosurgery alone, or chemotherapy when the primary tumor responds to anticancer drugs.¹ Novel therapies under clinical evaluation include dendritic cell vaccination, tyrosine kinase receptor inhibitors, oncolytic viruses, and other antiangiogenesis agents.³

Risk factors

The cause of most adult brain tumors is not known, and there are few established risk factors. Exposure to vinyl chloride may increase the risk of glioma. Infection with the Epstein-Barr virus, having AIDS, or receiving an organ transplant may increase the risk of primary CNS lymphoma. Genetic syndromes that raise risk include neurofibromatosis type 1 and type 2, von Hippel-Lindau disease, tuberous sclerosis, Li-Fraumeni syndrome, Turcot syndrome, and nevoid basal cell carcinoma syndrome.¹

Epidemiology and survival

In the United States, the incidence of malignant brain and other CNS tumors was 6.2 new cases per 100,000 people per year (SEER, 2017 to 2021), with a mortality rate of 4.4 deaths per 100,000 per year (2018 to 2022).³^•¹⁰ The American Cancer Society estimates about 24,740 new malignant brain or spinal cord tumors and 18,350 deaths in 2026; these cancers make up about 1% of new cancers in the US each year, and the lifetime chance of developing a malignant brain or spinal cord tumor is less than 1%.⁴ About 9 out of 10 brain and spinal cord tumors are diagnosed in adults, with an average age at diagnosis of 61 years.⁴ Approximately 74% of all brain tumors are benign, and more than 1.3 million Americans are estimated to be living with a primary brain tumor.²

Survival varies widely by tumor type and age. Based on CBTRUS data for people treated between 2004 and 2020, 5-year relative survival for low-grade diffuse astrocytoma is 79% at ages 15 to 39 versus 34% at age 40 and older; for glioblastoma, 28% versus 6%; for oligodendroglioma, 93% versus 79%; and for meningioma, 97% versus 88%.⁵ For all patients with malignant primary brain tumors, the 5-year relative survival is 34.8%, and for glioblastoma specifically it is 7.0%, with a median survival of 8 months.² SEER data for 2015 to 2021 give an overall 5-year relative survival of 33.0% for brain and other nervous system cancer.¹⁰

References

Topic: Encyclopedia › Life and health › Human health and medicine › Diseases and injuries › Nervous and sensory conditions › Brain and spinal tumors

Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Sep 30, 2026; Oct 21, 2026 · Last review: Oct 21, 2026

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