About 40% of non-small cell lung, pancreatic, and biliary tract cancer, 70% of mesothelioma and glioblastoma, and 35% of osteosarcoma, soft-tissue sarcoma, and T-cell acute lymphoblastic leukemia lack MTAP [4]–[11]. The gene discussed is MTAP; the disease is T-cell acute lymphoblastic leukemia.