"Molecular" glioblastoma

What it is

A "molecular" glioblastoma is an IDH-wildtype diffuse astrocytic glioma that is diagnosed as glioblastoma based on specific molecular markers — even if it does not yet show the most aggressive appearance under the microscope. The defining markers are a TERT promoter mutation, EGFR amplification, or combined chromosome 7 gain and 10 loss.

Understanding "Molecular" glioblastoma

Before the 2021 classification, glioblastoma was diagnosed mainly by aggressive appearance (such as necrosis and abnormal blood vessels). The 2021 classification recognized that some IDH-wildtype astrocytic tumors that look lower-grade nonetheless behave like glioblastoma — and that certain molecular markers identify them. So an IDH-wildtype tumor with any one of these markers (TERT mutation, EGFR amplification, or +7/−10) is now classified as glioblastoma even without the most aggressive appearance. This change ensures these aggressive tumors are recognized and treated appropriately, rather than being underestimated based on appearance alone. It is a clear example of molecular features overriding appearance. Understanding "molecular" glioblastoma clarifies how molecular markers can establish a glioblastoma diagnosis.

Why it matters

Understanding "molecular" glioblastoma helps patients and families see why a tumor that looks lower-grade can still be diagnosed as glioblastoma — molecular markers identify its aggressive nature, ensuring appropriate treatment.