24 showing that the MYCN gene was amplified 10–200‐fold in two primary retinoblastomas and in the Y79 cell line, but not in fibroblasts. Subsequently, Mairal et al. 14 assessed MYCN amplification karyotypically as double‐minute chromosomes and by PCR in four of 20 primary retinoblastomas. Further studies in a genetically engineered mouse model of human retinoblastoma demonstrated a 6–400‐fold amplification of MYCN in three of 16 aggressive retinoblastomas 25. Here, MYCN is linked to retinoblastoma.