IDH mutant tumors include oligodendrogliomas (expressing a 1p/19q codeletion), astrocytomas, IDH mutants, grade 2 and 3 (expressing P53 and ATRX mutations), and astrocytomas, IDH mutants, grade 4 (expressing the CDKN2A/B mutation). The gene discussed is CDKN2A; the disease is astrocytoma (excluding glioblastoma).