This study, known as the LIGHT trial, investigated the effectiveness of olaparib, a type of PARP inhibitor (poly(ADP-ribose)polymerase inhibitor), for treating platinum-sensitive relapsed ovarian cancer (PSROC). Researchers conducted a phase II, open-label, multicenter study with 272 patients. Patients were divided into groups based on their BRCA gene mutation (BRCAm) and homologous recombination deficiency (HRD) status. The four groups were: those with germline BRCAm (gBRCAm), somatic BRCAm (sBRCAm), HRD-positive tumors without BRCAm (genomic instability score ">=" 42), and HRD-negative tumors (genomic instability score "<" 42). The main goal was to measure the objective response rate (ORR), with secondary goals being disease control rate (DCR) and progression-free survival (PFS). Tumor samples were analyzed using specific assays. The study found that olaparib was effective across all groups. The highest ORRs were in the gBRCAm group (69.3%) and sBRCAm group (64.0%), with median PFS of 11.0 and 10.8 months, respectively. For patients without a BRCA mutation, the HRD-positive group showed better results (ORR 29.4%, median PFS 7.2 months) than the HRD-negative group (ORR 10.1%, median PFS 5.4 months). Overall, DCRs were high, ranging from 75.3% to 100%. Common side effects included nausea, fatigue, vomiting, and anemia, but the safety profile was consistent with prior olaparib studies. These findings suggest olaparib is a valuable treatment option, especially for patients with BRCA mutations or HRD-positive tumors, potentially reducing the need for traditional chemotherapy. However, the study was not randomized and lacked a comparator group.