IDH1 and astrocytoma (excluding glioblastoma): Two studies identified mutation of CDKN2A/B, an uncommon event in IDH-mutant astrocytoma (2.6%), to be associated with a poor prognosis similar to CDKN2A/B homozygous deletions on univariable analysis.89 The prognostic role of CDKN2A/B promoter methylation remains unclear.