In HRasV12-driven glioma and Eu-Myc-driven lymphoma, p53 restoration in tumors was effective but depended primarily on the presence of p19Arf upstream signaling to p53 (14, 50), and the restoration of p53 in KRas-driven lung tumors led to responses in malignant carcinomas but not in adenomas (15, 27), also in a manner dependent on p19Arf. The gene discussed is KRAS; the disease is central nervous system cancer.