Common Brain Tumors in Adults
Metastatic brain tumors are the most common intracranial tumors in adults, occurring approximately 10 times more frequently than primary brain tumors, with lung cancer accounting for half of all brain metastases. 1, 2
Primary Brain Tumors
Most Common Primary Tumors
Meningioma is the single most common primary brain tumor in adults overall, accounting for approximately 40% of all primary CNS tumors. 3, 2
- Meningiomas show strong female predominance with a 2:1 to 3:1 female-to-male ratio 4
- These tumors become increasingly common from age 35 years onward and remain the leading primary brain tumor through old age 4
- Most meningiomas (75-80%) are CNS WHO grade 1 (benign), with 15-20% being grade 2 and only 1-5% being grade 3 3
Most Common Malignant Primary Tumors
Glioblastoma (grade IV astrocytoma) is the most common primary malignant brain tumor in adults, accounting for 54% of all gliomas. 2
- Glioblastoma is the most lethal brain tumor, with only one-third of patients surviving 1 year and fewer than 5% living beyond 5 years 2
- The vast majority (90%) are IDH-wildtype, corresponding to de novo glioblastomas arising after age 55 years 5
- These tumors typically present with rapidly progressive symptoms over weeks to months, including increased intracranial pressure, seizures, or focal neurologic deficits 2
Anaplastic astrocytomas (grade III) are the second most common malignant glioma, accounting for 7% of all gliomas, with a 5-year survival rate of 27%. 2
Other Notable Primary Tumors
Pituitary adenomas represent another common benign primary brain tumor, particularly in younger adults transitioning from adolescence. 4, 6
- Together with meningiomas and vestibular schwannomas (acoustic neuromas), these benign tumors account for 30-40% of primary brain tumors 6
Anaplastic oligodendrogliomas are relatively rare but have a much better prognosis than anaplastic astrocytomas and glioblastomas, with half of patients alive at 5 years, due to marked sensitivity to chemotherapy and characteristic allelic losses of chromosomes 1p and 19q. 2
Secondary (Metastatic) Brain Tumors
Epidemiology and Sources
Brain metastases affect 8-10% of patients with cancer and occur in an estimated 20-40% of patients with systemic cancer. 1, 2
Primary lung cancers are the most common source of brain metastases, accounting for half of all intracranial metastases, though melanoma has the highest predilection to spread to the brain. 1
- Breast cancer is increasingly diagnosed with CNS involvement as systemic therapies improve 1
Distribution Patterns
Nearly 80% of brain metastases occur in the cerebral hemispheres, 15% in the cerebellum, and 5% in the brainstem. 1
- These lesions typically follow hematogenous spread to the gray-white junction where narrow blood vessels trap tumor emboli 1
- Most cases have multiple brain metastases evident on MRI 1
Age-Related Considerations
The incidence of primary brain tumors has been increasing over the past 30 years, especially in elderly persons. 2
- In young adults (age 20-34 years), medulloblastoma accounts for only 2% of CNS tumors, making it far less common than meningioma 4
- Glioblastoma becomes the second most common tumor (after meningioma) from middle age onward 4
- Pediatric tumors like pilocytic astrocytoma and medulloblastoma are characteristic of children and adolescents, not adults 4
Key Prognostic Factors
For high-grade gliomas, the most important prognostic factors are histologic diagnosis, age, and performance status. 2