CDKN2A and astrocytoma (excluding glioblastoma): CNS WHO grade 2 and 3 astrocytomas lack microvascular proliferation, tumor necrosis, and CDKN2A/2B mutation (which can be detected via fluorescent in situ hybridization, next-generation sequencing, and a number of other techniques) compared to CNS WHO grade 4 astrocytomas, which require the presence of at least one of these three histo-molecular attributes.11,12 Tumor grade has been correlated with patient survival.