There are over 100 recognized types of brain and central nervous system tumors. The World Health Organization maintains the official classification system, now in its fifth edition (published in 2021), which organizes these tumors into major families based on the type of cell they grow from and their genetic features. The number keeps growing as scientists identify new molecular subtypes: the 2021 update alone added 14 newly recognized tumor types just within the glioma and neuronal tumor categories.
Primary Tumors vs. Metastatic Tumors
Brain tumors fall into two broad camps. Primary brain tumors start in the brain itself or in its surrounding tissues. Metastatic brain tumors start somewhere else in the body, most commonly the lungs, breast, or skin, and spread to the brain. Metastatic brain tumors are actually more common than primary ones. When people ask about “types of brain cancer,” they’re usually asking about primary tumors, since metastatic tumors are classified by where they originated.
The Major Tumor Families
The WHO classification groups brain tumors into families based on which cells give rise to them. The largest and most clinically significant families include gliomas, meningiomas, embryonal tumors, nerve sheath tumors, germ cell tumors, and tumors of the pineal and pituitary regions. Each family contains multiple individual tumor types, and many of those types have subtypes of their own.
Gliomas
Gliomas develop from glial cells, the support cells that surround and nourish neurons. They’re the most common type of malignant primary brain tumor. The 2021 classification divides them into three main categories based on genetic markers rather than appearance alone:
- Astrocytomas grow from star-shaped glial cells. They range from slow-growing, low-grade tumors to aggressive high-grade forms. Whether the tumor carries a specific mutation in a metabolic enzyme called IDH determines both its classification and its likely behavior.
- Oligodendrogliomas arise from cells that produce the insulating coating around nerve fibers. These tumors are defined by the combination of an IDH mutation and a particular chromosomal change (loss of parts of chromosomes 1 and 19). They tend to grow more slowly and respond better to treatment than many other gliomas.
- Glioblastoma is the most aggressive and most common malignant brain tumor in adults. It is classified separately from other astrocytomas because it lacks the IDH mutation and carries its own distinct set of genetic features, including changes in chromosomes 7 and 10.
Additional glioma types include diffuse midline gliomas, which are defined by a specific alteration in a protein that controls gene activity. These tumors occur most often in children and tend to form in the brainstem, thalamus, or spinal cord.
Meningiomas
Meningiomas grow from the membranes that wrap around the brain and spinal cord. They’re the single most common primary brain tumor, accounting for roughly 38% of all primary central nervous system tumors and about half of all benign brain tumors. The vast majority, around 80%, are grade 1 (slow-growing and considered benign). About 17% to 18% are grade 2 (atypical, with a higher chance of returning after removal), and fewer than 2% are grade 3 (aggressive and cancerous).
Embryonal Tumors
Embryonal tumors develop from cells left over from early brain development. Medulloblastoma is the most well-known type and the most common malignant brain tumor in children, occurring at a rate of 5 to 6 cases per million children. It’s far rarer in adults, dropping to about 0.6 cases per million. Medulloblastoma itself is divided into at least four molecular subgroups, each with different biology and outlook. Other embryonal tumors include atypical teratoid/rhabdoid tumors, which are defined by the loss of a specific tumor-suppressing protein.
Pineal Region Tumors
The pineal gland, a small structure deep in the brain that helps regulate sleep cycles, can develop several distinct tumor types. Pineal parenchymal tumors grow from the gland’s own cells and range from slow-growing pineocytomas to fast-growing pineoblastomas. Germ cell tumors are among the most common tumors found in this region, particularly in children and young adults. The most common subtype, germinomas, often responds well to treatment. Less common nongerminomatous germ cell tumors tend to grow more aggressively. Papillary tumors of the pineal region are a separate, rare entity that develops near the gland but not from pineal cells themselves.
Other Tumor Types
Several additional families round out the classification. Nerve sheath tumors, such as schwannomas and neurofibromas, grow from the insulation around nerves. Ependymomas develop from cells lining the brain’s fluid-filled cavities and are now subdivided into multiple subtypes based on their molecular profile and location. Craniopharyngiomas grow near the pituitary gland and, while not cancerous, can cause serious problems by pressing on nearby structures that control hormones and vision. Pilocytic astrocytomas are low-grade tumors common in children, typically forming in the cerebellum, while in adults they’re more often found in other parts of the brain.
How Tumors Are Graded
Separate from type, brain tumors are assigned a WHO grade from 1 to 4. Grade 1 tumors are slow-growing and often curable with surgery alone. Grade 2 tumors grow slowly but can progress over time. Grade 3 tumors are actively malignant. Grade 4 tumors are the most aggressive, growing rapidly and often resistant to treatment. The same family of tumors can span multiple grades. An astrocytoma, for example, can be grade 2, 3, or 4 depending on its features.
Importantly, grade is no longer determined by how the tumor looks under a microscope alone. The 2021 classification system introduced rules that allow certain genetic markers to override microscopic appearance. A tumor that looks relatively calm under the microscope can be upgraded to grade 4 if it carries a specific chromosomal deletion linked to aggressive behavior. This shift means diagnoses are more precise and better predict how a tumor will actually behave.
Why the Number Keeps Growing
The total count of recognized brain tumor types has expanded with each new edition of the WHO classification. The main driver is molecular profiling. Tumors that once looked identical under a microscope are now split into separate types because they carry different genetic mutations, respond to different treatments, and have different survival rates.
DNA methylation profiling, a technique that reads chemical tags on a tumor’s DNA, can now identify tumor types that are invisible to traditional microscopy. This has led to the recognition of entirely new entities, such as high-grade astrocytomas with piloid features, and has split ependymomas into multiple molecular clusters tied to specific brain locations. Specific gene fusions and pathway alterations also define newer tumor types, particularly in pediatric patients.
The practical result is that two patients who might have received the same diagnosis 10 years ago could now be told they have fundamentally different tumors, with different treatment plans and different expected outcomes. The growing number of types reflects genuinely better understanding of the disease rather than arbitrary splitting.
Differences Between Children and Adults
Children and adults tend to develop different brain tumor types, and even when they share a diagnosis, the biology often differs. Medulloblastoma is overwhelmingly a childhood disease. Pilocytic astrocytoma, the most common brain tumor in children, typically appears in the cerebellum in kids but shows up in different brain regions in the rare adult cases. Glioblastoma, conversely, is primarily an adult tumor.
The 2021 classification formally separates “adult-type” and “pediatric-type” diffuse gliomas into distinct categories, acknowledging that childhood gliomas are driven by different molecular pathways than their adult counterparts. Pediatric gliomas more commonly involve alterations in growth signaling pathways and specific gene fusions, while adult gliomas are more often defined by the IDH mutation and chromosomal changes. This distinction matters because it directs children and adults toward different treatment strategies.