Simple SummaryThe therapeutic effect of Poly-ADP-ribose polymerase (PARP) inhibitor has been demonstrated in ovarian cancer patients withBRCAmutation or homologous recombination deficiency (HRD). HRD analysis at diagnosis determines treatment eligibility in ovarian cancer. In classifying the HRD patient group, different results may be observed depending on the test methods, and evidence of the possibility of differences in HRD prevalence between races was shown through representative clinical trial results. Accordingly, we are going to suggest the influence of individual treatment for ovarian cancer.AbstractAmong ovarian cancer patients withBRCAmutation or homologous recombination deficiency (HRD), the efficacy of Poly-ADP-ribose polymerase (PARP) inhibitors such as olaparib, niraparib, veliparib, and rucaparib has been proven in a number of clinical trials.BRCAmutation and HRD are currently indicated for PARP inhibitor maintenance treatment in ovarian cancer. HRD diagnostic tests examine various components, resulting in different HRD status definitions and, as a result, different treatment decisions. A number of HRD diagnostic tests exist, but test results provided by different companies may differ as they use different methods and different cutoffs. HRD prevalence difference was shown between PARP inhibitor maintenance trials. It is important to select an appropriate method that can present accurate HRD phenotypes to predict sensitivity to PARP inhibitors so that patients who are most likely to benefit from treatment are selected. Additionally, in the subset data of the PARP inhibitor maintenance trials, there was a difference in HRD prevalence by race as higher HRD prevalence in Japanese and Chinese ovarian cancer patients was shown. Further large-scale investigations on racial differences in HRD prevalence are needed and this may contribute to changes in determining the treatment plan and personalized treatment in ovarian cancer patients.