XRCC4 and retinoblastoma: Overexpression of ubiquitin-like with PHD and RING finger domains 1 (UHRF1) increases XRCC4 expression Conversely, the downregulation of XRCC4 renders retinoblastoma cells sensitive to etoposide treatment, indicating that XRCC4 is a key mediator of drug sensitivity following UHRF1 consumption in retinoblastoma cells.