Retinoblastoma, the most common primary intraocular malignancy of childhood, is initiated by mutation of both RB1 alleles in a single susceptible developing retinal cell, undergoes the limited proliferation of an RB1−/− retinal cell to form a non-malignant retinal tumor and consequently experiences uncontrolled proliferation and malignant transformation based on genetic or epigenetic alterations (1). This evidence concerns the gene RB1 and retinoblastoma.