An astrocytoma is a tumor that begins in the brain or spinal cord in small, star-shaped cells called astrocytes. The location of the tumor depends on the age of the person. In adults, astrocytomas most often arise in the cerebrum whereas in children, they may arise in the brain stem, cerebrum, and cerebellum. Astrocytomas are gliomas, brain tumors derived from glial, or supportive, cells. A far advanced (grade IV) astrocytoma is usually called a glioblastoma multiforme.