Glioblastomas (also called GBM) are malignant Grade IV tumours, where a large portion of tumour cells are reproducing and dividing at any given time. They are nourished by an ample and abnormal tumour vessel blood supply. The tumour is predominantly made up of abnormal astrocytic cells, but also contain a mix of different cell types (including blood vessels) and areas of dead cells (necrosis). Glioblastomas are infiltrative and invade into nearby regions of the brain. They can also sometimes spread to the opposite side of the brain through connection fibers (corpus callosum). It is exceedingly rare for glioblastomas to spread outside of the brain.
Glioblastomas may begin as a Grade IV tumour with no evidence of a lower grade precursor. De novo tumors are the most common form of glioblastoma and tend to be more aggressive and tend to affect older patients. Alternatively, secondary glioblastomas may progress from a lower-grade astrocytic tumours (Grade II or Grade III) and evolve into Grade IV tumours over time. In general, these tumours tend to be slower growing initially, but can progressively become aggressive. Glioblastomas are generally found in the cerebral hemispheres of the brain, but can be found anywhere in the brain. IDH mutant glioblastomas tend to arise preferentially in the frontal lobe.
Patients with glioblastomas develop symptoms rapidly due to mass effect from the tumour itself or from the fluid surrounding the tumour that causes further brain swelling. For example, common symptoms at diagnosis are related to the increased pressure in the brain (nausea, vomiting, and severe headaches which are typically worse in the morning). Patients can also present with neurological symptoms which are dependent on the tumour location (for example, weakness or sensory changes of face, arm or leg, balance difficulties and neurocognitive/memory issues). Other common presentation includes seizures.