BRCA1 and cancer: On the other hand, the defect in DNA damage repair in USP22 knockout cancer cell may be exploited to gain synthetic lethality therapy in combination of DNA damage causes such as irradiation, similar to the BRCA-PARP synthetic lethality, which show that PARP inhibitors effectively kill tumors defective in the breast cancer gene 1 and 2 (BRCA1/2) through the concept of synthetic lethality [47].