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Originally published March 11, 2025
Last updated March 11, 2025
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Primary brain tumors — tumors that start in or near the brain, whether cancerous or benign — are exceedingly rare in the United States. Less than 0.5% of the population is living with a primary brain tumor, according to the National Brain Tumor Society. And the American Cancer Society says the average person has less than a 1.0% chance of developing a malignant brain or spinal cord tumor in their lifetime.
What causes primary brain tumors to form in the first place? Are they hereditary?
“They are genetic in the sense that there are driver mutations, which can be inherited at birth, from which tumors can form,” says Frank Attenello, MD, MS, a surgeon-scientist at the USC Brain Tumor Center, part of Keck Medicine of USC, who specializes in treating and researching primary and metastatic brain tumors.
Hereditary conditions that actually lead to a brain tumor represent a small fraction of all cases — “about 5%, maybe even less,” stresses Dr. Attenello, who is also an associate professor of clinical neurological surgery at the Keck School of Medicine of USC.
The majority of brain tumors are metastatic, meaning the patient was diagnosed with cancer in another organ before it spread to the brain. Metastatic cases, also called secondary brain tumors, outnumber primary brain tumors by about 10 to 1.
As for primary brain tumors, several genetic syndromes can increase a patient’s risk of developing one.
Dr. Attenello says while these disorders can run in families, he also stresses that, in some cases, it’s undetermined what causes spontaneous cell mutations and resulting brain tumors.
Identified genetic disorders include:
“It’s somewhat unusual for an adult patient to be diagnosed with a primary brain tumor and only then discover they had a genetic syndrome,” Dr. Attenello says. “It’s more common for patients to be diagnosed with a genetic disorder at birth or early childhood.”
He emphasizes that patients with a known genetic syndrome are in a position to detect brain tumors at their earliest stages, when they are easiest to treat.
“In patients with known genetic tumor syndromes, with regular surveillance we’ll catch a tumor when it’s still small,” Dr. Attenello explains. “Catching a brain tumor early is the best way to ensure it doesn’t become a problem.”
If a brain tumor patient has a first-degree family member also diagnosed with a primary brain tumor, Dr. Attenello says he will usually refer brain tumor patients to genetic counseling to evaluate potential genetic syndromes associated with brain tumors.
Genetic counseling can start with taking a thorough personal and family history. If genetic testing is indicated and desired, samples are often drawn from the blood or potentially from a cheek swab.
“In the absence of strong suspicion of an inherited tumor predisposition, the risk of an inherited condition is relatively low,” Dr. Attenello says. “However, for those patients who remain concerned on behalf of their children, I will discuss options with neuro-oncology colleagues, and we may still offer referrals to genetic counseling.”
The signs of a brain tumor include common symptoms seen in many other illnesses and conditions such as:
“I don’t want to be an alarmist, because the vast majority of the time, patients with these symptoms don’t have a brain tumor,” Dr. Attenello reassures. “If you have a neurological symptom that is severe or doesn’t go away, however, don’t blow it off. And that’s what we see in patients with more advanced tumors — many of them ignored their symptoms.”
That said, Dr. Attenello emphasizes that a brain tumor isn’t the patient’s fault. They didn’t do anything wrong or somehow cause the tumor to form in the first place.
“There is ongoing exploration of what causes brain tumors. And we have a lot of therapies available to treat them, so I encourage my patients to focus on the good,” he says.
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