What molecular testing and treatment options should be considered for a patient with glioblastoma?

Molecular Testing and Treatment for Glioblastoma

For glioblastoma, perform molecular testing for MGMT promoter methylation status to guide treatment decisions, and consider comprehensive genomic profiling to identify rare actionable targets, though only BRAF V600E mutations have proven clinical benefit for targeted therapy in adult brain tumors. 1

Essential Molecular Testing

Standard Diagnostic Markers

The 2021 WHO classification defines glioblastoma as IDH-wild-type diffuse astrocytic glioma characterized by:

• IDH mutation status (must be wild-type for glioblastoma diagnosis)
• TERT promoter mutation
• EGFR amplification
• +7/-10 cytogenetic signature
• Microvascular proliferation and/or necrosis 2

Prognostic and Predictive Testing

MGMT promoter methylation is the single most important predictive biomarker:

• Determines benefit from temozolomide chemotherapy
• Guides treatment selection in elderly patients (>65-70 years)
• MGMT methylated tumors: use temozolomide chemoradiotherapy
• MGMT unmethylated tumors in elderly: consider radiotherapy alone (40 Gy in 2.67 Gy fractions) 2

Targeted Therapy Considerations

Proven Actionable Targets

According to the 2025 EANO guidelines, only BRAF V600E mutations have established clinical benefit (highest ESCAT tier) for targeted therapy in adult brain tumors 1. However, BRAF V600E mutations are exceedingly rare in glioblastoma.

Investigational Targets Worth Testing

The updated EANO guideline identifies these additional targets for consideration:

• NTRK gene fusions (tumor-agnostic FDA approval, but limited evidence in GBM)
• High tumor mutational burden (TMB-high) (regulatory approval exists but clinical benefit uncertain)
• FGFR alterations
• PTEN/PI3K pathway alterations
• RET fusions
• MTAP deletions
• IDH mutations (as therapeutic target, though by definition absent in glioblastoma) 1

Real-World Implementation Data

A Danish study implementing genomic profiling from 2016-2023 found:

• 41.4% of patients harbored alterations of interest
• Only 4.1% had high-tier actionable alterations (ESCAT I-II)
• Just 3.1% actually received targeted therapy
• Among treated patients: 20% overall response rate, 47% achieved stable disease
• Median duration of response: 12 months 3

This highlights a critical caveat: While comprehensive genomic profiling identifies alterations in many patients, very few translate to actual therapeutic benefit in glioblastoma.

Standard Treatment Approach

Newly Diagnosed Glioblastoma

The standard of care remains temozolomide chemoradiotherapy (54-60 Gy in 1.8-2 Gy fractions) for most patients 2

Age-based modifications:

• Patients >65-70 years with MGMT unmethylated tumors: radiotherapy alone (40 Gy in 2.67 Gy fractions)
• Patients >65-70 years with MGMT methylated tumors: either temozolomide chemoradiotherapy OR temozolomide alone 2

Recurrent Glioblastoma

Treatment options at progression include:

• Nitrosourea-based chemotherapy
• Temozolomide rechallenge (limited activity in MGMT unmethylated tumors)
• Bevacizumab (does not prolong survival but may provide symptomatic benefit)
• Re-irradiation (controversial, case-by-case basis)
• Second surgery (only if gross total resection achievable) 2

Important negative trial results:

• Nivolumab is NOT superior to bevacizumab in recurrent glioblastoma
• Nivolumab is NOT superior to temozolomide in newly diagnosed MGMT unmethylated glioblastoma
• Extending temozolomide from 6 to 12 cycles does NOT improve survival 2

Practical Algorithm for Molecular Testing

At diagnosis, obtain:

1. IDH mutation status (diagnostic requirement)
2. MGMT promoter methylation (treatment selection)
3. TERT promoter, EGFR amplification, +7/-10 signature (diagnostic confirmation)

Consider comprehensive genomic profiling (NGS panel) if:

• Patient has good performance status (KPS ≥70)
• Recurrent disease after standard therapy
• Access to clinical trials
• Younger patients (<50 years) where rare actionable alterations more likely

Do NOT delay standard treatment waiting for comprehensive genomic results—median turnaround time is 48 days, and actionable findings are rare 4

Critical Pitfalls to Avoid

• Do not withhold temozolomide based solely on MGMT unmethylated status in younger patients—combined chemoradiotherapy remains standard
• Do not pursue immunotherapy outside clinical trials—checkpoint inhibitors have failed in multiple phase III trials 2
• Do not assume systemic cancer targets apply to GBM—the blood-brain barrier, tumor microenvironment, and low mutational burden create unique resistance mechanisms 5, 6
• Recognize that tumor heterogeneity limits targeted therapy—spatial and temporal evolution drives resistance even when targets are identified 6, 7

The therapeutic landscape for glioblastoma remains dominated by surgery, radiotherapy, and temozolomide, with molecular testing primarily serving diagnostic and prognostic rather than therapeutic purposes in the vast majority of cases.