MDM2 and retinoblastoma: We do not find upregulation of MDM2 mRNA but robust expression of CDKN2A. Human cPR precursors express high levels of MDM2 and patient-derived retinoblastoma cells require functional MDM2 for survival which also suppresses CDKN2A/p14ARF-induced apoptosis in cultured human retinoblastoma cells [15].