MDM2 and retinoblastoma: However in retinoblastoma, TP53 mutation has not been reported, and alternative modes of p53 inactivation implicating MDM2 and MDM4 have been suggested but remain to be confirmed, since the expression of MDM2 in retinoblastomas is similar to retina [7-9] and MDM4 is situated in a region of frequent genomic gain (chromosome 1q32) that also contains the oncogene KIF14 [10].