Primary brain tumors arise from cells within the brain or its surrounding structures and represent approximately 1.4% of all new cancer diagnoses. The American Cancer Society estimates approximately 25,400 new malignant brain and spinal cord tumors are diagnosed in the United States each year, with roughly 18,760 deaths. Including benign tumors, over 94,000 primary brain tumors are diagnosed annually (Central Brain Tumor Registry of the United States). Brain tumors are the leading cause of cancer death in children under 15 and among the most challenging cancers to treat in adults.
The 2021 WHO Classification of Tumors of the Central Nervous System represents a paradigm shift, integrating molecular markers—particularly IDH mutation status and 1p/19q codeletion—alongside histology to define tumor types. This molecular reclassification has refined prognosis and is guiding the development of targeted therapies.
Major Types of Primary Brain Tumors
Glioblastoma (GBM)
The most common and aggressive primary malignant brain tumor in adults, classified as WHO grade 4. Glioblastoma (IDH-wildtype) accounts for approximately 49% of all malignant primary brain tumors. It is characterized by rapid growth, extensive infiltration into surrounding brain tissue, neovascularization, and central necrosis. GBM most commonly occurs in adults over 50 and has a median survival of approximately 15–18 months with the Stupp protocol and a five-year survival rate of approximately 6.8%.
Astrocytoma (IDH-Mutant)
Diffuse astrocytomas harboring IDH1 or IDH2 mutations are now classified separately from glioblastoma under the 2021 WHO classification. They are graded 2, 3, or 4 based on histological features (mitoses, necrosis, microvascular proliferation). IDH-mutant astrocytomas have significantly better prognosis than IDH-wildtype glioblastoma at every grade level, with grade 2 IDH-mutant astrocytoma having a median survival exceeding 10 years.
Oligodendroglioma (IDH-Mutant, 1p/19q-Codeleted)
Defined by the presence of both IDH mutation and 1p/19q codeletion, oligodendrogliomas account for approximately 5% of primary brain tumors. They are classified as WHO grade 2 or 3. Oligodendrogliomas are characteristically chemosensitive, particularly to the PCV regimen (procarbazine, CCNU/lomustine, vincristine), and have the best prognosis among adult diffuse gliomas, with median survival exceeding 14 years for grade 2 tumors.
Meningioma
The most common primary intracranial tumor overall, accounting for approximately 39% of all primary brain tumors. Meningiomas arise from the meninges (the membranes covering the brain and spinal cord) and are WHO grade 1 (benign) in approximately 80% of cases. Most meningiomas grow slowly and may be observed with serial imaging. Surgery is the primary treatment when intervention is needed, and radiation therapy is used for incompletely resected, recurrent, or higher-grade (grade 2–3) meningiomas.
WHO Grading System
| WHO Grade | Characteristics | Examples |
|---|---|---|
| Grade 1 | Slow-growing, well-circumscribed, low proliferative potential, possible cure with surgery alone | Pilocytic astrocytoma, most meningiomas, schwannoma |
| Grade 2 | Infiltrative, relatively slow-growing, tendency to recur and progress to higher grades | IDH-mutant astrocytoma (grade 2), oligodendroglioma (grade 2) |
| Grade 3 | Anaplastic features, increased mitotic activity, higher recurrence rate | IDH-mutant astrocytoma (grade 3), anaplastic oligodendroglioma |
| Grade 4 | Highly malignant, rapid growth, necrosis, neovascularization, poor prognosis | Glioblastoma (IDH-wildtype), IDH-mutant astrocytoma (grade 4), diffuse midline glioma |
Based on the 2021 WHO Classification of Tumors of the Central Nervous System (5th edition). Molecular markers now define tumor types alongside histology.
Other Notable Brain Tumors
Several additional primary brain tumor types warrant mention: Ependymoma arises from ependymal cells lining the ventricles and spinal cord central canal, representing approximately 3% of primary brain tumors. Medulloblastoma is the most common malignant brain tumor in children, classified into four molecular subgroups (WNT, SHH, Group 3, Group 4) with distinct prognoses. Schwannoma (particularly vestibular schwannoma/acoustic neuroma) is a benign nerve sheath tumor that can cause hearing loss and balance problems. Craniopharyngioma is a rare benign tumor arising near the pituitary gland that can cause significant hormonal deficiencies and visual impairment.
Risk Factors
- Ionizing radiation — The only firmly established environmental risk factor. Prior therapeutic cranial radiation, especially in childhood, significantly increases risk of meningioma and glioma decades later.
- Genetic syndromes — Neurofibromatosis type 1 (optic pathway glioma), neurofibromatosis type 2 (schwannomas, meningiomas), tuberous sclerosis (subependymal giant cell astrocytoma), Li-Fraumeni syndrome (gliomas), von Hippel-Lindau disease (hemangioblastoma), and Turner syndrome.
- Immunosuppression — Increased risk of primary CNS lymphoma, particularly in HIV/AIDS patients.
- Age — Glioblastoma incidence peaks in the 65–84 age group. Certain tumor types (medulloblastoma, pilocytic astrocytoma) are more common in children.
- Sex — Meningiomas are approximately twice as common in women; glioblastomas are 1.6 times more common in men.
Treatment Options
Surgery
Maximal safe surgical resection is the cornerstone of brain tumor treatment. The extent of resection is one of the strongest prognostic factors for gliomas. Modern neurosurgical techniques include:
- Awake craniotomy with cortical mapping — Allows real-time testing of language, motor, and cognitive function during tumor removal to minimize neurological deficits.
- Fluorescence-guided surgery (5-ALA) — The fluorescent dye 5-aminolevulinic acid (5-ALA/Gleolan) is taken up by high-grade glioma cells and fluoresces pink under blue light, helping surgeons distinguish tumor from normal brain tissue.
- Laser interstitial thermal therapy (LITT) — A minimally invasive MRI-guided laser ablation technique for deep-seated or recurrent tumors that are not amenable to open surgical resection.
- Neuronavigation and intraoperative MRI — Image-guided surgical tools improve accuracy of tumor localization and resection completeness.
The Stupp Protocol (Standard of Care for Glioblastoma)
The landmark Stupp protocol, established in 2005, remains the standard first-line treatment for newly diagnosed glioblastoma:
- Concurrent temozolomide and focal radiation therapy (60 Gy in 30 fractions over 6 weeks)
- Followed by adjuvant temozolomide (6–12 cycles)
This regimen improved median survival from 12.1 to 14.6 months and increased the two-year survival rate from 10% to 27%. MGMT promoter methylation status is a key predictor of temozolomide benefit—patients with methylated MGMT have median survival exceeding 21 months.
Tumor Treating Fields (TTFields)
Optune (NovoTTF-200A) delivers low-intensity, alternating electric fields to the tumor region via transducer arrays worn on the scalp. When added to maintenance temozolomide, TTFields improved median survival from 16.0 to 20.9 months in the EF-14 trial. TTFields are FDA-approved for newly diagnosed and recurrent glioblastoma.
Radiation Techniques
Focal radiation therapy using IMRT or proton beam therapy is standard for gliomas, targeting the tumor bed with a margin while minimizing dose to surrounding healthy brain. Stereotactic radiosurgery (SRS) is used for small, well-defined lesions such as brain metastases and selected meningiomas. Whole-brain radiation therapy (WBRT) is reserved for multiple brain metastases but carries significant neurocognitive risks; hippocampal-avoidance WBRT and memantine have been shown to mitigate cognitive decline.
Chemotherapy for Non-GBM Gliomas
For IDH-mutant astrocytomas and oligodendrogliomas, the PCV regimen (procarbazine, CCNU, vincristine) and temozolomide are the primary chemotherapy options. The CATNON trial demonstrated that adjuvant temozolomide significantly improves survival in grade 3 IDH-mutant astrocytomas without 1p/19q codeletion. For oligodendrogliomas, PCV after radiation improved median overall survival from 7.8 to 14.7 years in the RTOG 9402 trial.
Targeted Therapy and Emerging Treatments
- Bevacizumab (Avastin) — Anti-VEGF antibody approved for recurrent glioblastoma. Improves progression-free survival and reduces corticosteroid dependence but has not demonstrated overall survival benefit.
- IDH inhibitors — Vorasidenib (a dual IDH1/IDH2 inhibitor) showed significant improvement in progression-free survival for grade 2 IDH-mutant gliomas in the INDIGO trial and received FDA approval in 2024, representing the first targeted therapy for low-grade gliomas.
- PCV chemotherapy — Procarbazine, CCNU (lomustine), and vincristine. Standard adjuvant chemotherapy for anaplastic oligodendroglioma and increasingly used for IDH-mutant astrocytomas, based on long-term survival benefits demonstrated in the RTOG 9402 and EORTC 26951 trials.
Supportive Care and Symptom Management
Brain tumor management extends beyond anti-cancer treatment to address the significant neurological and quality-of-life impacts of both the disease and its treatment:
- Corticosteroids (dexamethasone) — Used to reduce peritumoral edema and associated symptoms. Long-term use carries significant side effects including weight gain, hyperglycemia, myopathy, and immunosuppression.
- Antiepileptic drugs (AEDs) — Seizures occur in 20–40% of brain tumor patients. Levetiracetam is preferred due to its lack of cytochrome P450 interactions with chemotherapy agents. Prophylactic AEDs are not recommended for patients without a seizure history.
- Venous thromboembolism (VTE) prophylaxis — Brain tumor patients have a 20–30% risk of VTE. Anticoagulation with low-molecular-weight heparin or direct oral anticoagulants is safe and indicated for most brain tumor patients with VTE.
- Neurocognitive rehabilitation — Cognitive deficits from tumor and treatment (particularly whole-brain radiation) can be addressed through neuropsychological assessment and targeted rehabilitation programs.