The WHO classification recommends diagnostic testing for CDKN2A/CDKN2B homozygous in IDH-mutant astrocytomas showing histological features of anaplasia corresponding to CNS WHO grade 3, but not for IDH-mutant astrocytomas with histological features corresponding to CNS WHO grade 2 tumors [30], as the latter generally lack CDKN2A/CDKN2B homozygous deletion [41] (Table 1). The gene discussed is CDKN2B; the disease is astrocytoma (excluding glioblastoma).