Oligodendroglial tumors are given two grades. (Grading, instead of staging, is used to assess the likelihood that a brain tumor will spread. The higher the grade, the more dangerous the tumor.) Grade II oligodendroglial tumors, called oligodendrogliomas, grow and spread slowly. Anaplastic oligodendrogliomas, on the other hand, are grade III tumors that grow quickly, and may grow in several places in the brain.