The present application relates to the field of cancer, particularly that of cancers with high MDM4 protein levels (such as melanoma, breast, colon or lung cancers, glioblastoma, retinoblastoma, etc.). It is shown herein that direct and selective inhibition of MDM4, e.g., by antisense RNA, leads to growth inhibition of cancer cells and sensitization to chemo or targeted therapies. Also provided are simple ways of determining which patients are most amenable for such treatment by comparing specific transcript levels.