IDH1 and astrocytoma (excluding glioblastoma): While in most other blue books, low grade and high grade examples of tumors, such as low/high grade chondrosarcomas, are listed in their own respective chapters and considered different ‘types”, grade 2 IDH-mutant astrocytomas (low grade) and grade 4 IDH-mutant astrocytomas (high grade) are listed under the same tumor type.