IDH1 and glioblastoma: Loss of p16 expression was observed in 57% (36/63) of IDH-wt GBM, 33% (2/6) of IDH-mutant astrocytomas (grade 4), 40% (2/5) of IDH-mutant astrocytomas (grade 3), 29% (5/17) of IDH-mutant 1p/19q codeleted OG (grade 3), 67% (6/9) of H3K27-altered diffuse gliomas, 38% (3/8) of wt pediatric diffuse gliomas, and in the only case of PXA with anaplasia.