IDH1 and astrocytoma (excluding glioblastoma): Fu et al. (2013) noted that AB did not present the typical cytogenetic features of astrocytoma and ependymoma. ABs do not share mutation signatures with low-grade (WHO grade II) diffuse astrocytoma (IDH1/2 and TP53) or ependymomas (IDH1, TP53, and IDH R132H immunoreactivity).