The PEG10 gene (encoding the Paternally Expressed Gene 10 Protein, reported to have a role in cell differentiation and apoptosis) was downregulated in extraocular RB samples in both CPL and MKI67+ PhrD cells, indicating a possible loss of differentiation in cells of extraocular RB tumors. The gene discussed is PEG10; the disease is retinoblastoma.