RB1 and astrocytoma (excluding glioblastoma): Lastly, the tumor suppressors INK4A and ARF, positive regulators of RB and p53 respectively, are encoded at the CDKN2A locus, which is deleted in approximately 50% of high‐grade astrocytomas and a significant percentage of anaplastic oligodendrogliomas as well 8, 10, 53, 77.