Definition and epidemiology
Glioblastoma is a WHO grade 4 astrocytoma characterized by microvascular proliferation and necrosis. It represents approximately 45-50% of all malignant primary brain tumors and 15% of all primary brain tumors in adults.
Incidence is approximately 3-4 cases per 100,000 person-years in the United States and Europe. GBM predominantly affects adults with a peak incidence between 55 and 65 years of age. Males are affected slightly more frequently than females with a ratio of approximately 1.6:1. The tumor is more common in white populations compared to other ethnic groups.
GBM can be classified into primary (de novo) glioblastoma, which arises without evidence of a pre-existing lower-grade lesion and accounts for approximately 90% of cases, and secondary glioblastoma, which develops from progression of lower-grade diffuse astrocytomas and represents about 10% of cases. Secondary GBM typically occurs in younger patients (mean age around 45 years) and has distinct molecular features.
- Glioblastoma is the most common malignant primary brain tumor in adults (WHO grade 4).
- Classic MRI shows ring-enhancing mass with central necrosis and vasogenic edema.
- Histology requires microvascular proliferation and necrosis; IDH-wildtype defines true glioblastoma.
- MGMT promoter methylation predicts better response to temozolomide chemotherapy.
- Standard treatment is maximal safe resection followed by concurrent radiation and temozolomide (Stupp protocol).
- Tumors frequently cross the corpus callosum creating a 'butterfly glioma' appearance.
- Median survival is 15-18 months despite aggressive multimodal therapy.
- Bevacizumab is used for recurrent disease but does not improve overall survival.
Etiology and risk factors
The etiology of glioblastoma remains largely unknown. Most cases are sporadic with no clear environmental or lifestyle risk factors identified.
Established risk factors include:
- Ionizing radiation: The only consistently proven environmental risk factor. Therapeutic cranial irradiation (especially in childhood) increases risk after a latency period of 10-15 years.
- Genetic syndromes: Rare hereditary conditions account for fewer than 5% of cases. These include neurofibromatosis type 1, Li-Fraumeni syndrome (TP53 germline mutations), Lynch syndrome, and Turcot syndrome.
- Age: Incidence increases with age, peaking in the sixth and seventh decades.
- Sex: Males have a moderately increased risk compared to females.
Unproven or inconsistent associations include cell phone use, electromagnetic fields, dietary factors, and occupational exposures. Large epidemiological studies have not established causal relationships with these factors.
Primary and secondary GBMs have distinct molecular pathways. Primary GBM frequently harbors EGFR amplification, TERT promoter mutations, and PTEN loss. Secondary GBM typically shows IDH1 or IDH2 mutations and TP53 mutations, arising from lower-grade precursors.
Pathophysiology
Glioblastoma arises from the malignant transformation of glial cells, likely neural stem cells or progenitor cells in the subventricular zone. The tumor is characterized by rapid proliferation, aggressive invasion along white matter tracts, prominent angiogenesis, and resistance to apoptosis.
Molecular classification
The 2021 WHO classification emphasizes molecular features. IDH-wildtype glioblastoma (the vast majority of primary GBM) is molecularly defined and carries worse prognosis. IDH-mutant astrocytoma, grade 4 (formerly secondary GBM with IDH mutation) is now classified separately and has somewhat better outcomes.
Key molecular alterations in IDH-wildtype GBM include:
- TERT promoter mutations: Present in 70-80%, associated with telomerase activation
- EGFR alterations: Amplification or mutations in 40-60%
- PTEN loss: Occurs in 30-40%
- TP53 mutations: Present in 25-30%
- CDKN2A/B deletion: Found in 50-60%
- MGMT promoter methylation: Present in 40-45%, predictive of temozolomide response
Histopathological features
Defining characteristics include microvascular proliferation (glomeruloid tufts of endothelial cells) and necrosis (often in serpentine patterns with pseudopalisading tumor cells around necrotic foci). The tumor shows marked nuclear atypia, high mitotic activity, and infiltrative growth. Tumor cells invade along blood vessels, through white matter tracts, and across the corpus callosum, making complete surgical resection impossible.
Clinical features
Clinical presentation depends on tumor location, size, and rate of growth. Symptoms typically evolve over weeks to months.
Common presenting symptoms
- Headache (40-50%): Often worse in the morning, progressive, may be associated with nausea and vomiting due to increased intracranial pressure
- Seizures (30-40%): May be focal or generalized; often the presenting symptom in tumors involving the cortex
- Cognitive or personality changes (30-40%): Memory impairment, confusion, behavioral changes, especially with frontal lobe involvement
- Focal neurological deficits (40-60%): Motor weakness (hemiparesis), sensory deficits, aphasia, visual field defects, or cranial nerve palsies depending on location
- Nausea and vomiting (20-30%): Related to increased intracranial pressure
Physical examination
Findings are variable and location-dependent:
- Motor deficits: Hemiparesis or monoparesis
- Sensory changes: Hemisensory loss or neglect
- Visual field deficits: Homonymous hemianopia with occipital or temporal involvement
- Aphasia: Expressive or receptive with dominant hemisphere involvement
- Papilledema: Late finding indicating increased intracranial pressure
- Cognitive impairment: Executive dysfunction, memory deficits, altered mental status
Symptoms may progress rapidly due to tumor growth, surrounding edema, or hemorrhage within the tumor.
Diagnosis
Diagnosis requires neuroimaging followed by histopathological and molecular confirmation.
Neuroimaging
MRI with contrast is the gold standard. Characteristic features include:
- T1-weighted post-contrast: Irregular, thick ring enhancement with central necrosis
- T2/FLAIR: Surrounding vasogenic edema and infiltration extending beyond the enhancing margin
- Mass effect: Midline shift, sulcal effacement, ventricular compression
- Location: Most commonly in the cerebral hemispheres (frontal and temporal lobes most frequent); can cross the corpus callosum ("butterfly glioma")
- Diffusion-weighted imaging: Restricted diffusion in hypercellular regions
- Perfusion imaging: Elevated relative cerebral blood volume indicating angiogenesis
CT scan with contrast shows a heterogeneous mass with ring enhancement and central hypodensity. CT is less sensitive than MRI but useful in emergency settings or when MRI is contraindicated.
Histopathology and molecular testing
Stereotactic biopsy or surgical resection provides tissue for diagnosis. Histology shows:
- Microvascular proliferation and necrosis (required for WHO grade 4)
- High cellularity with marked nuclear atypia
- High mitotic activity
- Pseudopalisading necrosis
Molecular testing is essential for classification:
- IDH1/IDH2 mutation status: IDH-wildtype defines glioblastoma; IDH-mutant is classified as astrocytoma grade 4
- MGMT promoter methylation: Predictive biomarker for temozolomide response
- Additional markers (EGFR amplification, TERT promoter mutation, chromosome 7 gain/10 loss) support diagnosis
Additional workup
- Complete blood count, comprehensive metabolic panel, coagulation studies: Preoperative assessment
- Corticosteroids: Often started before surgery to reduce vasogenic edema
- Antiepileptic drugs: If seizures are present
Differential diagnosis
The differential diagnosis of a ring-enhancing brain mass includes:
Primary CNS tumors
- Anaplastic astrocytoma (grade 3): Shows contrast enhancement but lacks necrosis; requires histology to distinguish
- CNS lymphoma: Usually shows homogeneous enhancement in periventricular regions; more common in immunocompromised patients
- Metastatic brain tumor: Often multiple lesions at gray-white junction; history of systemic cancer; more discrete margins
Infections
- Brain abscess: Ring-enhancing lesion with smooth, thin wall; restricted diffusion in center; clinical context of fever and systemic infection
- Toxoplasmosis: Multiple ring-enhancing lesions; common in HIV/AIDS patients with CD4 <100
- Tuberculoma: Ring-enhancing mass with tuberculosis history; meningeal involvement may be present
Inflammatory/demyelinating
- Tumefactive demyelinating lesion: Large demyelinating plaque that may enhance; typically incomplete rim; younger patients with relapsing symptoms
Vascular
- Subacute infarct: Can show ring enhancement 1-4 weeks post-stroke; follows vascular territory
- Resolving hematoma: History of trauma or bleeding; evolving signal characteristics over time
Other
- Radiation necrosis: In patients with prior brain irradiation; can be indistinguishable from tumor; perfusion imaging and PET help differentiate
Histopathological examination with molecular testing is required for definitive diagnosis.
Management
Treatment is multimodal involving surgery, radiotherapy, and chemotherapy. Management aims to maximize survival and quality of life while recognizing the poor prognosis.
Surgical management
Maximal safe resection is the initial treatment when feasible. Goals include:
- Tissue diagnosis and molecular characterization
- Cytoreduction to decrease tumor burden
- Relief of mass effect
- Improvement of symptoms
Extent of resection correlates with survival; gross total resection (when safely achievable) is associated with longer progression-free and overall survival. Intraoperative tools include neuronavigation, intraoperative MRI, fluorescence-guided surgery (5-aminolevulinic acid), and awake craniotomy for eloquent cortex tumors.
Stereotactic biopsy is performed when the tumor is in an eloquent or deep location where resection carries high risk.
Adjuvant therapy (Stupp protocol)
The standard of care for newly diagnosed glioblastoma in patients with good performance status:
Concurrent chemoradiotherapy:
- Radiotherapy: Focal external beam radiation (60 Gy in 30 fractions over 6 weeks) to the tumor bed plus 2 cm margin
- Temozolomide: Given daily during radiation
Adjuvant chemotherapy:
- Temozolomide: Administered for 6-12 cycles (typically 6 months)
MGMT promoter methylation predicts better response to temozolomide.
Tumor-treating fields
Tumor-treating fields (TTFields) is a FDA-approved device therapy that delivers low-intensity alternating electric fields. When added to maintenance temozolomide, it modestly improves progression-free and overall survival.
Recurrent disease
Options are limited and chosen based on prior treatment, performance status, and tumor location:
- Re-resection: If surgically accessible and patient has good functional status
- Bevacizumab: Anti-VEGF antibody; may reduce edema and improve symptoms; approved for recurrent GBM
- Lomustine (CCNU): Alkylating agent used in some protocols
- Clinical trials: Should be considered at all stages
- Best supportive care: Focus on symptom management and quality of life
Supportive care
- Corticosteroids (dexamethasone): Reduce vasogenic edema and mass effect
- Antiepileptic drugs: For seizure management; prophylaxis not routinely recommended
- Venous thromboembolism prophylaxis: High risk of deep vein thrombosis
- Palliative care: Early integration improves quality of life and should be discussed at diagnosis
Complications and prognosis
Complications
Neurological deterioration:
- Progressive tumor growth causing worsening deficits
- Seizures (new-onset or refractory)
- Cognitive decline and personality changes
- Increased intracranial pressure with herniation risk
Treatment-related:
- Surgical: Infection, hemorrhage, stroke, worsening neurological deficits
- Radiation: Early (fatigue, scalp erythema), delayed (radiation necrosis, cognitive decline, endocrine dysfunction)
- Chemotherapy: Myelosuppression (thrombocytopenia, leukopenia), nausea, fatigue, opportunistic infections (Pneumocystis pneumonia)
Systemic:
- Venous thromboembolism (up to 30% of patients)
- Steroid-related complications: hyperglycemia, immunosuppression, myopathy, osteoporosis
Prognosis
Glioblastoma carries a poor prognosis despite aggressive treatment. Median overall survival is approximately 15-18 months with standard therapy (surgery, radiation, and temozolomide).
Prognostic factors associated with better survival:
- Younger age (typically <50 years)
- Good performance status (Karnofsky Performance Status ≥70)
- Extent of resection (gross total vs. subtotal)
- MGMT promoter methylation
- IDH-mutant status (now classified as astrocytoma grade 4, not glioblastoma)
Survival statistics:
- 1-year survival: Approximately 40-50%
- 2-year survival: Approximately 25-30%
- 5-year survival: Approximately 5-10%
IDH-mutant astrocytoma grade 4 has significantly better prognosis with median survival of 30-40 months. Nearly all patients experience tumor recurrence, typically within 7-10 months of initial diagnosis. Focus on quality of life, symptom management, and advance care planning is essential throughout the disease course.
Practice questions
1. A 62-year-old man presents with progressive headaches and left-sided weakness over 6 weeks. MRI shows a 4 cm ring-enhancing mass confined to the right frontal lobe with central necrosis and surrounding vasogenic edema. Biopsy reveals high-grade astrocytoma with microvascular proliferation, necrosis, and pseudopalisading cells. Molecular testing shows IDH-wildtype and MGMT promoter methylation. What is the most appropriate next step in management?
2. A 58-year-old woman with newly diagnosed glioblastoma completed maximal resection followed by radiation and 6 months of temozolomide. She now presents 8 months later with worsening confusion and right hemiparesis. MRI shows a new enhancing mass at the resection cavity margin. She has a Karnofsky Performance Status of 70. Which treatment option has proven benefit for this clinical scenario?
3. A 45-year-old man undergoes biopsy of a left temporal lobe ring-enhancing mass. Pathology shows a high-grade astrocytoma with necrosis and microvascular proliferation. Molecular testing reveals IDH1 R132H mutation and TP53 mutation. MGMT promoter is methylated. What is the most likely diagnosis and expected prognosis compared to the more common variant?
Frequently asked questions
What causes glioblastoma?
The cause of glioblastoma is largely unknown in most cases. The only proven environmental risk factor is ionizing radiation, particularly therapeutic cranial irradiation during childhood. Fewer than 5% of cases are associated with hereditary cancer syndromes such as neurofibromatosis type 1, Li-Fraumeni syndrome, or Lynch syndrome. Most glioblastomas arise sporadically without identifiable genetic or environmental causes. Cell phone use and electromagnetic fields have not been proven to cause glioblastoma.
What are the first symptoms of glioblastoma?
The most common initial symptoms of glioblastoma include persistent headaches (often worse in the morning), new-onset seizures, and progressive neurological deficits such as weakness or speech difficulties. Cognitive changes like memory problems, confusion, or personality changes may also be early signs, especially with frontal lobe tumors. Symptoms typically develop over weeks to months and worsen progressively. The specific presentation depends on the tumor's location in the brain.
How is glioblastoma diagnosed?
Glioblastoma is diagnosed using MRI with contrast, which typically shows a ring-enhancing mass with central necrosis and surrounding edema. Definitive diagnosis requires tissue sampling through either surgical resection or stereotactic biopsy. Pathological examination must demonstrate microvascular proliferation and necrosis, the hallmarks of grade 4 glioma. Molecular testing for IDH mutation status and MGMT promoter methylation is essential for classification and treatment planning. IDH-wildtype status confirms true glioblastoma.
Is glioblastoma curable?
No, glioblastoma is not curable with current treatments. Despite aggressive multimodal therapy including surgery, radiation, and chemotherapy, nearly all patients experience tumor recurrence. The median survival is approximately 15-18 months, and five-year survival is only 5-10%. Treatment goals focus on prolonging survival, maintaining quality of life, and managing symptoms. Ongoing research into immunotherapy, targeted therapies, and novel treatment approaches continues in hope of improving outcomes.
Glioblastoma vs brain metastases — what is the difference?
Glioblastoma is a primary brain tumor arising from brain glial cells, while brain metastases are cancers that spread to the brain from other body sites. Metastases are often multiple and located at the gray-white junction, whereas glioblastoma is typically a single mass with infiltrative borders. Brain metastases usually have more discrete margins on imaging and a known history of systemic cancer. Glioblastoma requires molecular testing showing IDH-wildtype status and specific histological features including pseudopalisading necrosis. Treatment approaches differ significantly between the two conditions.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: C71
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.