IDH1 and astrocytoma (excluding glioblastoma): Interestingly, in non-central nervous system cancers such as leukemia, it has been hypothesized that CDKN2A/B is haplo-insufficient, where hemizygous loss would not produce adequate production of protein necessary for tumor suppression.21,22 We see a similar phenomenon amongst IDH1/2-mutant astrocytoma, with one copy loss of CDKN2A/B demonstrating a significantly worse prognosis, which was similar to that of grade 4 tumors with two copy loss.