USP7 and neoplasm: In addition, the H&E staining showed that FEN1 overexpression might cause typically histological changes in the xenografts (Figure 8D). Furthermore, immunohistochemical staining demonstrated that FEN1 overexpression significantly elevated the expression of Ki67, MDM2, and USP7 of the xenograft tumor tissues, while the exogenous FEN1 remarkably decreased P53 expression (Figure 8E).