Oct 21, - Tumors can occur at any age, but many types are most common in a certain age group. In adults, gliomas and meningiomas are the most common. Gliomas come from glial cells such as astrocytes, oligodendrocytes, and ependymal cells. Glioblastomas are the most aggressive type of primary brain tumor. May 8, - In adults, primary brain tumors are much less common than are secondary brain tumors, in which cancer begins elsewhere and spreads to the.