About 26% of all primary brain tumors are cancerous (malignant), while roughly 74% are non-cancerous (benign). That means roughly three out of four brain tumors diagnosed in the United States are not cancer. However, the full picture is more nuanced than that ratio suggests, because even non-cancerous brain tumors can cause serious problems depending on where they grow.
How the Numbers Break Down
The Central Brain Tumor Registry of the United States (CBTRUS), the most comprehensive national database, tracked nearly 490,000 primary brain and central nervous system tumors diagnosed between 2018 and 2022. Of those, about 128,865 were malignant and 360,853 were non-malignant. That works out to an annual incidence rate of 6.86 per 100,000 people for malignant tumors and 19.19 per 100,000 for non-malignant ones.
If you look at prevalence, meaning all the people currently living with a brain tumor diagnosis, the malignant share drops even further. As of the end of 2019, about 1.3 million Americans were living with a primary brain tumor, and only 14% of them had a malignant one. That lower figure reflects the fact that people with non-cancerous tumors tend to survive much longer, so they accumulate in the population over time.
The Most Common Types
Meningiomas are the single most common primary brain tumor, making up about 30% of all brain tumors. These grow from the membranes surrounding the brain and are overwhelmingly benign. Only 1% to 4% of meningiomas are classified as cancerous (grade 3). Because meningiomas are so common and so rarely malignant, they heavily tilt the overall statistics toward the benign side.
On the malignant end, glioblastoma is the most aggressive and well-known type. It’s classified as a grade 4 tumor. Five-year survival rates for glioblastoma are roughly 28% for adults aged 15 to 39, but drop to about 6% for those over 40. Other malignant types fare better. Oligodendrogliomas, for instance, have a five-year survival rate of 93% in younger adults and 79% in those over 40. Ependymomas, another type, have survival rates above 90% regardless of age group.
The range is enormous. “Malignant brain tumor” is not a single diagnosis with a single outlook. Some are slow-growing and highly treatable, while others are among the most difficult cancers in medicine.
How Brain Tumors Are Graded
Brain tumors are classified using the World Health Organization’s grading system, which assigns grades 1 through 4. Lower grades (1 and 2) are generally slow-growing and less likely to spread into surrounding tissue. Higher grades (3 and 4) grow faster, are more abnormal under a microscope, and are considered malignant.
Grading in the brain works differently than cancer staging in other organs. A grade 2 tumor in the brain might still be called “low-grade” but can behave aggressively depending on its molecular features. The most recent WHO classification, updated in 2021, now incorporates genetic markers alongside what the tumor looks like under a microscope. Certain genetic deletions can push a tumor to grade 4 even if it doesn’t show the classic microscopic signs of aggressive growth, like new blood vessel formation or tissue death. This means grading has become more precise but also more complex.
Why “Benign” Doesn’t Always Mean Safe
The word “benign” is reassuring in most parts of the body, but the brain is different. The skull is a fixed, enclosed space. A non-cancerous tumor that grows slowly can still compress healthy brain tissue, block the flow of cerebrospinal fluid, and raise pressure inside the skull. Depending on location, even a small benign tumor can cause seizures, vision loss, personality changes, or problems with movement and balance.
A benign tumor sitting near the brainstem, which controls breathing and heart rate, can be life-threatening regardless of its grade. And some benign tumors sit in spots where surgical removal is extremely difficult, meaning they may require long-term monitoring or repeated treatment even though they aren’t cancerous. Johns Hopkins Medicine notes that benign brain tumors located in a vital area of the brain can be life-threatening. So while the statistics clearly show that most brain tumors are not cancer, having a non-cancerous brain tumor is still a serious medical situation.
What About Tumors That Spread to the Brain
All of the statistics above refer to primary brain tumors, meaning tumors that originate in the brain itself. But a large number of brain tumors are actually metastatic, meaning they started as cancer somewhere else in the body (most commonly the lungs, breast, skin, colon, or kidney) and spread to the brain. Metastatic brain tumors are always cancerous by definition, since only malignant cells can travel from one organ to another.
Metastatic brain tumors are estimated to outnumber primary brain tumors significantly, though exact figures are harder to pin down because they’re often tracked under the original cancer type rather than as a separate brain tumor diagnosis. If metastatic tumors were included in the overall count, the percentage of brain tumors that are cancerous would be considerably higher than 26%.
Survival Varies Widely by Type and Age
Five-year survival rates for brain tumors span an enormous range. At one end, meningiomas have a 97% five-year survival rate in younger adults and 88% in those over 40. At the other end, glioblastoma’s five-year survival sits at just 6% for people over 40.
Age is one of the strongest predictors of outcome. Across nearly every tumor type, younger patients have significantly better survival rates. For low-grade diffuse astrocytomas, five-year survival is 79% for those aged 15 to 39 but 34% for those 40 and older. For anaplastic astrocytomas, it’s 64% versus 21%. This pattern holds consistently, though the gap is smaller for slower-growing tumor types.
The type of tumor matters more than whether it’s technically classified as benign or malignant. A grade 2 tumor in a surgically accessible location has a very different outlook than a grade 4 glioblastoma deep in the brain. If you or someone you know has been diagnosed, the specific tumor type, grade, molecular profile, and location will tell you far more than the benign-versus-malignant label alone.