A 50-year-old patient has a cerebral tumor biopsy showing microvascular proliferation, geographic necrosis with pseudopalisading, and high mitotic rate. Molecular analysis reveals EGFR amplification, PTEN loss, and TERT promoter mutation. IDH mutation is absent. This tumor is classified as:

• A IDH-mutant glioblastoma (secondary GBM), WHO grade 4
• B IDH-wildtype glioblastoma (primary GBM), WHO grade 4 ✓
• C Anaplastic astrocytoma, IDH-wildtype, WHO grade 3
• D Diffuse midline glioma, H3K27M-mutant

Explanation

IDH-wildtype glioblastoma (primary or de novo GBM) is the most common primary malignant brain tumor in adults, arising without prior lower-grade lesion. The 2021 WHO CNS classification requires IDH-wildtype astrocytoma to be classified as glioblastoma, WHO grade 4, if it shows EGFR amplification, TERT promoter mutation, or chromosome 7 gain/10 loss — even without classic histological features. Pseudopalisading necrosis reflects hypoxia-driven cell migration. IDH-mutant GBMs arise from lower-grade gliomas and carry better prognosis.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.