The homozygous deletion of cyclin-dependent kinase inhibitor 2A/B (CDKN2A/B) at the 9p21 chromosome occurs in the early stages of GBM, and since methylthioadenosine phosphorylase (MTAP) is close to the CDKN2A tumor suppressor sites, this leads to the co-deletion of MTAP [72,73]. The gene discussed is CDKN2A; the disease is glioblastoma.