IDH1 and astrocytoma (excluding glioblastoma): At the same time, only those OPC-like cells that demonstrate activation of molecular programs of cell plasticity and cell response to hypoxia, localized mainly in the tissue of astrocytomas, IDH-mut, grade 3 and grade 4, and in the tissue of oligodendrogliomas, IDH-mut, grade 3, can be a source of mesenchymal transformation.