Glioblastoma multiforme (GBM) is the most common glioma—a type of brain cancer. This cancer starts in the glial cells, which are cells that help nerve cells work.

This condition can develop suddenly. It can also develop from a lower grade, less cancerous brain tumor. Most cases are located in the cerebral hemisphere of the brain. The cancer can also begin in the spinal cord or brain stem.

Brain Tumor
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GBM originates from astrocytes, which are a type of glial cell. The factors that cause normal-functioning astrocytes to become cancerous is not well understood.