USP22 and neoplasm: Furthermore, subcutaneous injection of normal USP22‐expressing or USP22‐overexpressing SW 1990 cells into the left flank of nude mice for a xenograft assay, followed by mouse treatment with or without MDM2 inhibitor, revealed that USP22 overexpression and MDM2 inhibitor treatment could both slow tumor growth; the combined treatment group showed additional inhibition of tumor growth (Fig. 6F–H).