TP53 and astrocytoma (excluding glioblastoma): For example, common molecular alterations identified in low-grade oligodendrogliomas and astrocytomas are allelic loss of 1p and 19q and mutations in p53, respectively, whereas grade 3 and 4 astrocytomas typically are driven by alterations in phosphoinositide 3-kinase (PI3K), EGFR, VEGF, and PTEN signaling (2).