In our study, decreased expression of the gene PDC (encoding Phosducin, a photoreceptor-specific protein participating in visual phototransduction and photoreceptor metabolism) was observed in all three major cell types in extraocular RB samples, indicating a loss of differentiation and photoreceptor expression signature in extraocular RB tumors, suggesting a higher degree of malignancy. The gene discussed is PDC; the disease is retinoblastoma.