Glioblastoma Multiforme (GBM) also called glioblastoma, is a fast-growing glioma that develops from star-shaped glial cells called astrocytes and oligodendrocytes that support the health of the nerve cells within the brain. GBM is often referred to as a grade IV astrocytoma. These are the most invasive type of glial tumors, rapidly growing and commonly spreading into nearby brain tissue