PARP1 and ovarian cancer: Although BRCA1 and BRCA2 (BRCA1/2) mutation status were regarded as an important indicator in the application of PARPi in ovarian cancer patients [10], there were still 40–70% of patients not responding expectedly to Olaparib as a result of drug resistance through multiple mechanisms such as restoration of BRCA1 or BRCA2 protein functionality by secondary mutations, BRCA1/2 promoter methylation reversion, BRCA1/2 hypomorph overexpression, PARP1 expression deficiency, drug efflux, or acquisition of new mutations in other DDR genes [30–33].