CLSPN and neoplasm: In addition to its well characterized role in regulating HDM2 and p53 levels, USP7 modulates the stability of a number of additional proteins such as FOXO4, PTEN, claspin and UHRF1 [36, 44–47]; thus, inhibiting USP7 has the potential for direct anti-tumor activity against both p53 wild type and p53 mutant tumors [48].