We previously reported that CEP-1347, a drug developed for the treatment of Parkinson’s disease that has a well-characterized safety profile, acted as a novel MDM4 inhibitor for p53 stabilization and activation by suppressing MDM4 expression in retinoblastoma, glioblastoma, and meningioma cells [16,17,18,19]. The gene discussed is MDM4; the disease is retinoblastoma.