HDAC9 and retinoblastoma: As poorly differentiated RB is associated with multiple high‐risk histopathologic factors to some extent (Kashyap et al., 2012), the negative role of UHRF1 in photoreceptor differentiation may present a novel insight into the tumor‐promoting functions of UHRF1 in RB cells in addition to its implication in ROS homeostasis and protective roles against HDAC inhibitor‐induced cell death (Fig. 8).