CDKN2A and astrocytoma (excluding glioblastoma): Since homozygous CDKN2A deletion accounts for most CDKN2A mutations and has a prognosis equivalent to that of IDH-mutant astrocytoma with other CDKN2A mutations (and hemizygous CDKN2A loss), it can be used as a surrogate marker for determining prognosis [18].