Brain tumors are abnormal growths of cells inside the skull, either within the brain itself, in the protective layers surrounding it, or in nearby structures like the pituitary gland or spinal cord. Around 322,000 new malignant brain tumors are diagnosed worldwide each year, and over 1.3 million people in the United States alone are living with a primary brain tumor. Some brain tumors are cancerous and fast-growing, while others are benign and may never cause problems.
Primary vs. Secondary Brain Tumors
Brain tumors fall into two broad categories based on where they originate. Primary brain tumors start in the brain or its surrounding tissues. They can be benign (noncancerous) or malignant (cancerous), and the most common benign type in adults is the meningioma, a slow-growing tumor that forms in the thin layers covering the brain. Meningiomas account for roughly one-third of all primary brain tumors.
Secondary brain tumors, also called brain metastases, start as cancer somewhere else in the body and spread to the brain through the bloodstream. These tumors are made of the same cell type as the original cancer. If lung cancer spreads to the brain, for instance, the brain tumor is composed of lung cancer cells, not brain cells. The cancers most likely to spread to the brain are lung, breast, kidney, melanoma, and colorectal cancer.
Common Types and How They’re Graded
The World Health Organization grades brain tumors on a scale from 1 to 4. Lower grades (1 and 2) grow slowly and are less likely to spread. Higher grades (3 and 4) are aggressive, grow quickly, and are harder to treat. Grading now incorporates both what the cells look like under a microscope and specific genetic changes found in the tumor’s DNA, meaning two tumors that look similar can receive different grades based on their molecular profile.
Glioblastoma is the most common malignant brain tumor in adults, making up about 15% of all brain tumors. It’s a grade 4 tumor that primarily affects people between ages 45 and 70, and it grows rapidly. Survival after diagnosis is typically less than 15 months, though a molecular subtype that tends to affect younger adults carries a somewhat better outlook.
On the other end of the spectrum, meningiomas are usually grade 1, grow slowly, and often require nothing more than monitoring. Oligodendrogliomas and ependymomas fall somewhere in between, with generally more favorable outcomes than glioblastomas.
In children, the tumor landscape looks different. The most common pediatric brain tumors are pilocytic astrocytomas, medulloblastomas, and malignant gliomas. Even when a child and an adult have the same tumor type, the symptoms, behavior of the tumor, and treatment outcomes often differ.
Symptoms by Tumor Location
Brain tumor symptoms depend heavily on where the tumor sits, because each region of the brain controls different functions. Some tumors cause obvious problems early on. Others grow for months or years in “quieter” areas before producing noticeable symptoms.
Frontal lobe: Difficulty concentrating, personality changes, loss of inhibition (saying inappropriate things or laughing at the wrong moments), trouble with decision-making and planning, weakness on the opposite side of the body, and loss of smell.
Temporal lobe: Hearing problems, difficulty recognizing objects or emotions in others, memory loss, seizures, and sensations of strange smells that aren’t there.
Parietal lobe: Trouble judging distances, poor hand-eye coordination, difficulty recognizing faces, numbness on the opposite side of the body, and problems with reading, writing, or understanding words.
Occipital lobe: Vision problems, including difficulty identifying objects or colors, and loss of vision on one side.
Cerebellum: Balance problems, loss of coordination, difficulty walking, vomiting, stiff neck, and trouble with fine motor tasks like buttoning a shirt.
Brain stem: Unsteadiness, facial weakness, double vision, and difficulty speaking or swallowing.
Many of these symptoms overlap with far more common conditions like migraines, inner ear problems, or stress. A single episode of dizziness or forgetfulness is rarely a tumor. Persistent or worsening symptoms, especially combinations from the lists above, are what raise concern.
What Causes Brain Tumors
For most people, no clear cause is ever identified. The strongest confirmed environmental risk factor is exposure to high-dose ionizing radiation, the kind used in radiation therapy to the head for a previous cancer. Occupational lead exposure has been linked to an increased risk of meningiomas specifically.
Genetics play a role in a small percentage of cases. Certain inherited conditions, like neurofibromatosis (caused by mutations in the NF1 gene), significantly raise the risk. Researchers have also identified variations in genes involved in DNA repair, cell growth regulation, and immune function that may make some people more susceptible, though these factors alone rarely cause tumors.
One finding that has puzzled researchers: people with a history of allergies appear to have a lower risk of glioma. The reasons aren’t fully understood, but it may relate to how an overactive immune system interacts with abnormal cell growth in the brain.
How Brain Tumors Are Diagnosed
Diagnosis usually starts with imaging. An MRI or CT scan can reveal an abnormal mass, its size, and its location. But imaging alone often can’t determine exactly what type of tumor is present or whether it’s cancerous.
When imaging leaves questions, a biopsy provides the definitive answer. There are two main approaches. A stereotactic biopsy uses a small opening in the skull and a needle guided by MRI or CT imaging to reach the tumor with high precision. An open biopsy, called a craniotomy, involves removing a section of skull to access the tumor directly. In either case, a pathologist examines the tissue under a microscope and runs molecular tests to classify the tumor and assign its grade.
Treatment Options
Surgery is the first-line treatment for most brain tumors. The goal is to remove all of the tumor, but that isn’t always possible. When a tumor is intertwined with critical brain structures, surgeons remove as much as they safely can, a procedure called subtotal resection. Even partial removal can relieve symptoms by reducing pressure inside the skull.
Radiation therapy typically follows surgery for malignant tumors. External beam radiation is the most common form, usually delivered in short daily sessions five days a week for two to six weeks. The radiation is aimed at the area surrounding the tumor to destroy remaining cancer cells. When multiple tumors are present, whole-brain radiation may be necessary. A more focused option called radiosurgery delivers a concentrated dose in one session or a few sessions, targeting the tumor while sparing more healthy tissue.
For some slow-growing benign tumors like small meningiomas, active monitoring with periodic MRI scans is all that’s needed. Treatment only begins if the tumor starts to grow or cause symptoms.
Survival Rates by Tumor Type
Five-year survival varies enormously depending on tumor type and age at diagnosis. Based on data from people treated between 2004 and 2020:
- Meningioma: 97% for ages 15 to 39, 88% for ages 40 and older
- Oligodendroglioma: 93% for younger adults, 79% for those over 40
- Ependymoma: 95% for younger adults, 91% for those over 40
- Low-grade astrocytoma: 79% for younger adults, 34% for those over 40
- Glioblastoma: 28% for ages 15 to 39, 6% for ages 40 and older
Age is one of the most powerful predictors of outcome across nearly every tumor type. Younger patients consistently fare better, partly because they tend to tolerate aggressive treatment more easily and partly because their tumors more often carry molecular features associated with slower growth. The gap is especially striking for glioblastoma, where five-year survival is nearly five times higher in younger adults compared to those diagnosed after 40.