Genetically, MYCN-amplified RB1+/+ retinoblastomas show fewer copy number changes compared with classic RB1–/– retinoblastomas,6 and they are hypothesized to originate in an earlier retinal precursor cell6 compared with RB1–/– retinoblastomas, which are thought to develop from a cone-photoreceptor precursor cell.7 Here, RB1 is linked to retinoblastoma.