MTAP and glioblastoma: MTAP is ubiquitously expressed in normal tissues; however, because MTAP gene locates close to tumor suppressor gene CDKN2A, MTAP homologous deletion occurs frequently in cancers such as 40% in glioblastomas; 25% in melanomas, urothelial carcinomas and pancreatic adenocarcinomas; 15% in non-small cell lung carcinomas (Kryukov et al., 2016).