Multiple recent studies have shown that IDH-mutant astrocytomas accumulate increasing CNA with recurrence [133, 177], as they progress from a mean CNA level of 9.3 ± 0.5% (~ 290 Megabase pairs [Mbp]) in CNS WHO grade 2 to 20.9 ± 1.8% (~ 650 Mbp) in CNS WHO grade 4 [48, 173–177, 190], and/or with the development of defined high-grade molecular features, such as homozygous CDKN2A loss [150]. The gene discussed is IDH1; the disease is astrocytoma (excluding glioblastoma).