To identify a novel pharmacotherapy for aggressive meningiomas with the intention to further characterize CEP-1347 as an MDM4 inhibitor, we herein examined its effects on malignant meningioma cells, because meningiomas reportedly have a low incidence of p53 mutation and, thus, may have functionally inactivated p53, similar to retinoblastoma and glioblastoma [14,15]. Here, TP53 is linked to retinoblastoma.