MYCN and retinoblastoma: We compared the relative levels of expression of SKP2, p27, pRb, and ppRb proteins in four MYCN‐amplified and one MYCN‐low retinoblastomas by immunohistochemistry (IHC) staining of tumor sections with antibodies specific for these proteins (Table 3 and Fig. 4, Figure S1 and Table S4).