Brain tumors show considerable phenotypic and genetic heterogeneity.
Primary brain tumor and metastatic brain tumors comprise a heterogeneous group of CNS malignancies, varying in histological features 1) phenotypic presentation 2) ,cell origin, and tumor grade as designated by the World Health Organization Classification of Tumors of the Central Nervous System.
Within the brain itself, the involved cells may be neurons or glial cells (which include astrocytes, oligodendrocytes, and ependymal cells). Brain tumors may also spread from cancers primarily located in other organs (metastatic tumors).