Cancer can cause seizures, and in some cases a seizure is the very first sign that a tumor exists. New-onset seizures are the presenting symptom in roughly 20 to 40 percent of people eventually diagnosed with a brain tumor, and seizures occur at some point during the illness in 40 to 60 percent of patients with gliomas. But the relationship between cancer and seizures goes beyond tumors sitting directly in the brain. Metabolic disruptions, immune reactions triggered by distant cancers, and even certain cancer treatments can all push the brain toward seizure activity.
How Common Are Seizures in Cancer Patients
The numbers depend heavily on the type of cancer and where it is growing. Among patients with primary brain tumors called gliomas, seizures are remarkably common. Lower-grade, slower-growing gliomas are especially seizure-prone: studies consistently report that the majority of people with low-grade gliomas experience seizures at some point. Higher-grade tumors like glioblastomas carry a lower but still significant seizure rate. Even patients who have never had a seizure face about a 20 percent chance of developing one over the course of their disease if they have a primary or metastatic brain tumor.1PubMed Central. The use of prophylactic anticonvulsants in patients with brain tumours-a systematic review
When cancer spreads to the brain from elsewhere in the body, the seizure risk is somewhat lower but far from trivial. A large population-level study found that about 10 percent of patients with brain metastases developed seizures.2PubMed Central. Seizures Among Patients With Brain Metastases: A Population- and Institutional-Level Analysis That figure may undercount the true rate: when researchers specifically monitored patients with metastatic brain tumors using continuous brain-wave recordings, they found clinically definite seizures in about 29 percent of patients and captured seizure activity on the recordings themselves in roughly 19 percent.3Journal of Clinical Neurophysiology. Seizures in Patients with Metastatic Brain Tumors: Prevalence, Clinical Characteristics, and Features on EEG The gap between population-level and monitored rates suggests that many seizures in cancer patients go unrecognized, particularly subtle ones that do not involve dramatic convulsions.
Among metastatic cancers, melanoma and lung cancer carry the highest seizure risk when they reach the brain.4PubMed. Epilepsy in brain metastasis: an emerging entity Breast cancer and colorectal cancer also commonly metastasize to the brain, though their seizure rates tend to be somewhat lower.
Why Tumors Trigger Seizures
A seizure happens when neurons in the brain fire in abnormal, synchronized bursts. Tumors set this off through several overlapping pathways, not just by pressing on brain tissue.
One of the most studied mechanisms involves a chemical called glutamate, the brain’s main excitatory signaling molecule. Gliomas actively pump out abnormally high levels of glutamate through a specific transporter on their cell surfaces.5PubMed Central. Glutamate release by primary brain tumors induces epileptic activity This flood of glutamate overstimulates neurons in the surrounding brain tissue. Making matters worse, the healthy support cells around the tumor lose their ability to clean up excess glutamate, and immune cells in the area may release even more of it. The tumor also weakens the blood-brain barrier, allowing additional seizure-promoting substances to leak into brain tissue from the bloodstream.6PubMed Central. Glutamate and tumor-associated epilepsy: glial cell dysfunction in the peritumoral environment
Tumor genetics also matter. Certain mutations found in slower-growing gliomas, particularly changes in the IDH1 gene, are independently linked to a higher rate of seizures. A meta-analysis found a significant association between IDH1 and IDH2 mutations and seizures before surgery, specifically in patients with low-grade gliomas.7PubMed. Association Between IDH1 and IDH2 Mutations and Preoperative Seizures in Patients with Low-Grade Versus High-Grade Glioma: A Systematic Review and Meta-Analysis One study found that the IDH1 mutation was an independent risk factor for seizures, roughly quintupling the odds compared to tumors without the mutation.8PubMed. IDH1 mutation predicts seizure occurrence and prognosis in lower-grade glioma adults These mutations lead to overproduction of a metabolite called D-2-hydroxyglutarate, which resembles glutamate closely enough to excite neurons on its own.9PubMed Central. Multi-omics technologies and molecular biomarkers in brain tumor-related epilepsy
The paradox here is worth noting: the genetic features that make some gliomas more seizure-prone are often the same features associated with slower tumor growth and longer survival. Patients with IDH-mutated low-grade gliomas tend to live longer than those with wild-type tumors, but they may spend years dealing with difficult-to-control seizures. About 22 percent of IDH-mutated low-grade glioma patients developed seizures that stopped responding adequately to medication.10Neuro-Oncology Advances. Pharmacoresistant seizures and IDH mutation in low-grade gliomas
Where the Tumor Sits Makes a Big Difference
Not all brain regions are equally seizure-prone. Tumors involving the temporal lobe, the area on each side of the brain behind the temples, are more than twice as likely to cause seizures as tumors in other locations.11PubMed Central. Morphological Characteristics of Brain Tumors Causing Seizures The temporal lobe is particularly susceptible because it is a major hub for memory and emotional processing, and its neural circuits are easily disrupted. In one surgical series, 54 percent of brain lesions causing hard-to-treat seizures were located in the temporal lobe, and all patients with temporal lobe tumors had complex partial seizures.12PubMed. Intracranial, intraaxial, space-occupying lesions in patients with intractable partial seizures: an anatomoclinical, neuropsychological, and surgical correlation
Frontal lobe tumors also frequently cause seizures, though these may look different clinically. A seizure originating in the frontal lobe might involve sudden stiffening of a limb, jerking movements on one side of the body, or brief episodes where a person seems to “freeze” and lose awareness. Tumors deeper in the brain or in the back of the skull tend to be less seizure-prone, though they can certainly still cause them.
What the Signs Actually Look Like
When people think of seizures, they usually picture someone falling and convulsing. That type, called a generalized tonic-clonic seizure, does happen with brain tumors, but it is not the most common presentation. Many tumor-related seizures are focal, meaning they start in one area of the brain and produce symptoms tied to what that area normally does.
Focal seizures can look deceptively subtle:
- Motor symptoms: Involuntary twitching or jerking in one hand, arm, or side of the face. Sometimes the movement “marches” from one body part to an adjacent one over seconds.
- Sensory symptoms: Tingling, numbness, or a strange sensation running through one side of the body. Visual disturbances like flashing lights or partial loss of vision on one side.
- Awareness changes: Staring spells where the person seems awake but is unresponsive. They may perform automatic, purposeless movements like lip-smacking, picking at clothing, or fumbling with objects.
- Emotional or cognitive episodes: Sudden unexplained fear, a rising feeling in the stomach, déjà vu, or a strange smell or taste that isn’t there. These are particularly common with temporal lobe tumors.
A focal seizure can evolve into a generalized convulsion if the abnormal electrical activity spreads across both hemispheres. When this happens, the focal symptoms serve as a warning, sometimes lasting only seconds before the person loses consciousness. These warning symptoms can offer a clue about where the tumor is located, which is diagnostically useful.
One red flag that clinicians watch for is a new-onset seizure in an adult who has never had one before, especially someone over 40. While seizures have many causes, a first seizure in middle age or later warrants brain imaging to rule out a tumor. This is one of the most common ways brain tumors are discovered in the first place.
Seizures Without a Tumor in the Brain
Cancer does not have to be in or near the brain to cause seizures. There are at least two major pathways by which a tumor elsewhere in the body can trigger seizure activity.
The first is metabolic disruption. Cancer and its treatments can throw off blood chemistry in ways that lower the seizure threshold. Causes include low blood sugar, abnormal sodium or calcium levels, organ failure, and a condition called tumor lysis syndrome where dying cancer cells flood the bloodstream with their contents.13PubMed. Seizures and epilepsy in cancer: etiologies, evaluation, and management A study of cancer patients with altered mental status found that metabolic dysfunction contributed in nearly half of cases, and low oxygen levels were present in 43 percent.14JAMA Neurology. Altered Mental Status in Patients With Cancer These metabolic seizures tend to resolve once the underlying imbalance is corrected, unlike seizures caused by structural brain damage.
The second pathway is paraneoplastic syndromes. These occur when the immune system, activated by a tumor, mistakenly attacks healthy brain tissue. The tumor itself may be in the lung, ovary, thymus, or another organ, but the immune assault targets neurons. Paraneoplastic limbic encephalitis, for example, inflames the memory and emotion centers of the brain. In one study of patients with lung cancer who developed this condition, seizures were among the most common presenting symptoms.15PubMed. Paraneoplastic epilepsy Paraneoplastic seizures are especially tricky because they can appear months before the underlying cancer is diagnosed, leading to a confusing period where a patient has new seizures but no apparent brain abnormality on imaging.
When Cancer Treatment Itself Causes Seizures
Some cancer therapies carry their own seizure risk. Certain chemotherapy drugs, particularly platinum-based agents, have been associated with neurological side effects including seizures and a condition called posterior reversible encephalopathy syndrome, which involves brain swelling, confusion, and seizures.16Nature Reviews Clinical Oncology. Neurological adverse effects caused by cytotoxic and targeted therapies
Radiation therapy to the brain can also be a delayed cause. Radiation necrosis, where healthy brain tissue is damaged by prior radiation, occurs in roughly 4 to 30 percent of patients and typically appears 6 to 24 months after treatment. The damaged tissue can act as a seizure focus, sometimes long after the original tumor has been addressed. This wide range reflects the variability in radiation doses, techniques, and tumor types treated.
These treatment-related seizures are important to distinguish from tumor-caused seizures because they carry different implications. A new seizure after radiation could mean the tumor has come back, but it could also be radiation necrosis, and the two require very different management.
Managing Seizures in Someone with Cancer
Seizure treatment in cancer patients adds complexity that doesn’t exist in ordinary epilepsy care. The same anti-seizure medications that work in other settings are used here, but the choice of which one matters more because of drug interactions with chemotherapy.
Older anti-seizure drugs often speed up or slow down the liver enzymes that metabolize chemotherapy agents, potentially making cancer treatment less effective or more toxic. Newer anti-seizure medications generally have fewer of these interaction problems, which is why they are often preferred in cancer patients.17PubMed Central. Seizures and cancer: drug interactions of anticonvulsants with chemotherapeutic agents, tyrosine kinase inhibitors and glucocorticoids Getting this balance right requires close coordination between the oncology and neurology teams.
For seizures caused directly by the tumor, surgery often provides the most lasting relief. Complete removal of the tumor gives the best chance of long-term seizure control, especially in lower-grade gliomas. Radiation and chemotherapy can add further benefit by suppressing regrowth.18Current Treatment Options in Neurology. Treatment Considerations in Tumor-Related Epilepsy In some cases, seizure control becomes a primary goal of surgery even when the tumor itself is slow-growing and might otherwise be monitored.
One important clinical question is whether patients with brain tumors who haven’t yet had a seizure should take anti-seizure medication preventively. The evidence has generally not supported routine prophylactic use, and most guidelines advise against it. The medications carry side effects including fatigue, cognitive dulling, and mood changes, and the data haven’t shown a clear benefit in preventing a first seizure.1PubMed Central. The use of prophylactic anticonvulsants in patients with brain tumours-a systematic review
How Seizures Affect Daily Life with Cancer
Beyond the physical danger of the seizures themselves, the impact on daily functioning can be substantial. Higher seizure frequency and generalized seizures significantly limit a patient’s ability to leave home and drive vehicles.19PubMed Central. Influence of Epilepsy on the Quality of Life of Patients with Brain Tumors In many places, driving restrictions after a seizure last months or longer, which is a major loss of independence for someone already coping with cancer treatment. The same study found that a proportion of patients with frequent generalized seizures continued to drive anyway, highlighting a serious safety gap.
Memory problems compound the difficulty. Seizures, the medications used to control them, and the tumor itself can all impair memory independently. Patients frequently report that memory dysfunction is one of the most disruptive aspects of their condition, more so in some cases than the seizures themselves.19PubMed Central. Influence of Epilepsy on the Quality of Life of Patients with Brain Tumors The anti-seizure medications can add to this burden, with patients perceiving their side effects as significantly disruptive.
When to Repeat Testing and What Gets Checked
If someone with a known cancer develops a new seizure, the evaluation usually includes brain imaging and often an EEG, a recording of the brain’s electrical activity. But the workup doesn’t always give answers on the first pass. A case report illustrated how a glioblastoma grew rapidly enough to appear on a repeat MRI done just weeks after a previous scan that had shown only subtle EEG abnormalities. The authors emphasized the importance of repeating both EEG and imaging within a short interval when the initial EEG shows something abnormal.20PubMed Central. Rapidly grown glioblastoma discovered on repeat MRI after pathologic EEG
For a first seizure in someone not known to have cancer, the imaging is equally critical. An MRI with contrast is the standard because it picks up small tumors that CT scans might miss. Blood work to check for metabolic causes is also routine. If a paraneoplastic syndrome is suspected, specific antibody tests can identify the immune attack, though these tests take time to return and not all antibodies have been characterized yet.
What Caregivers Need to Know
Witnessing a loved one’s seizure is frightening, and research shows that caregivers of brain tumor patients often feel unprepared for it. A qualitative study found that nearly all caregivers expressed difficulty knowing when to call emergency services during a seizure.21PubMed. “It’s Not Just the Seizures”: Brain Tumor Caregivers’ Experiences and Educational Needs in Out-of-Hospital Seizure Management Caregivers of patients who had not yet experienced a seizure were significantly less prepared to manage one than those who had already been through it, which suggests a gap in proactive education.
Most caregivers preferred to receive seizure-related training after the initial diagnosis rather than at the time of it, when they were already overwhelmed. They wanted written and online resources, with most preferring graphics or videos showing what seizures look like and what to do.21PubMed. “It’s Not Just the Seizures”: Brain Tumor Caregivers’ Experiences and Educational Needs in Out-of-Hospital Seizure Management The practical guidance for witnessing a seizure is the same regardless of cause: keep the person safe from injury, do not put anything in their mouth, time the seizure, and call emergency services if it lasts longer than five minutes or if it is a first seizure.
Seizure Control in Palliative and End-of-Life Care
As brain tumors progress or cancer reaches an advanced stage, seizure management takes on different priorities. Patients may lose the ability to swallow pills, which creates a logistical problem since most anti-seizure medications are oral. Alternative routes of delivery become essential. Medications can be given through buccal (inside the cheek), intranasal, or subcutaneous routes, and intravenous access is possible through long-term devices even in home or hospice settings.22PubMed. Management of prolonged epileptic seizures and status epilepticus in palliative care patients
One medication that has drawn particular interest for end-of-life seizure care is levetiracetam given subcutaneously, because it does not cause the heavy sedation that older drugs like midazolam and phenobarbital produce. A combined analysis of over 130 reported cases suggested that subcutaneous levetiracetam may have a role in managing seizures during the final days of life, with oral-to-subcutaneous conversion done at a one-to-one ratio.23PubMed. Subcutaneous Levetiracetam for the Management of Seizures at the End of Life: An Audit and Updated Literature Review The evidence remains limited to case series rather than controlled trials, but the clinical rationale is compelling: preventing seizures without unnecessarily sedating someone in their final days preserves whatever quality of interaction remains.24BMJ Supportive & Palliative Care. Subcutaneous levetiracetam for the management of seizures at the end of life
Emerging Biomarkers and Future Directions
Researchers are working to predict which brain tumor patients will develop seizures before they actually happen. Beyond the IDH mutations already discussed, several other molecular markers have shown promise. The BRAF V600E variant, known for its role in melanoma and some pediatric brain tumors, appears to promote seizure activity through separate pathways in neurons and tumor cells. Certain small RNA molecules, particularly miR-128, may be inversely associated with seizure risk, meaning lower levels could signal higher vulnerability. A protein called SV2A, which is also the target of levetiracetam, is being explored as a potential biomarker.9PubMed Central. Multi-omics technologies and molecular biomarkers in brain tumor-related epilepsy
None of these markers are ready for routine clinical use yet, and the field is still working through whether they can reliably identify at-risk patients early enough to intervene. But the eventual goal is appealing: knowing at the time of tumor diagnosis whether a given patient is likely to develop seizures could guide decisions about preventive medication, surgical aggressiveness, and monitoring intensity. For patients and families already dealing with a cancer diagnosis, any advance warning that seizures are coming would be genuinely useful preparation.