Background: Olaparib demonstrated its efficacy to prolong progression-free survival (PFS) in platinum-sensitive relapsed ovarian cancer (PSROC) patients (L-MOCA study). Almost half of OC patients harbor homologous recombination deficiencies (HRD). However, there is lack of the HRD prevalence in Asian PSR population. Meanwhile, Immunological processes play a key role in tumorigenesis and PD-L1 status may hinder an effective antitumor immune response in OC. Herein, we analyzed HRD and PD-L1 status in Asian patients with PSROC, and explored Olaparib response to different HRD status. Methods: In this exploratory analysis of L-MOCA trial, HRD and PD-L1 status were analyzed from patients with PSROC. Residual DNA samples of 193 patients were analyzed for HRD status with a local developed HRD assay (Teddy Laboratory, Shanghai, China, which determines two major components, tBRCA1/2 status and LOH score, HRD positive indicates the presence of a deleterious or suspected deleterious BRCA mutation or LOH score ≥0.4). The remaining formalin fixation and paraffin embedded samples were used for PD-L1 expression analysis by immunohistochemistry with SP263. Descriptive statistics were summarized for HRD status, PD-L1 expression status and PFS by different HRD status subgroups. Results: 193 of 224 patients had residual DNA for HRD test. Patients clinical characteristics were similar between those with and without residual DNA for HRD test, in terms of age (mean age 55.5y Vs 54.2y), FIGO stage (stage III 68.9% Vs 61.3%, stage IV 12.4% Vs 22.65%), and time to disease progression to Last prior Platinum Based Chemotherapy (6-12m: 39.9% Vs 41.9%; > 12m: 59.6% Vs 54.8%). Among 193 patients with HRD test conducted, proportion of HRD+ BRCAm, HRD+ BRCAwt, HRD- and HRD unknown were 37.3%, 28.0%, 14.5% and 20.2%, separately. mPFS of the above subgroups was 20.1 months, 15.8 months, 9.2 months and 16.4 months, respectively (Table1). 200 of 224 patients were available for PD-L1 expression analysis. 184 (92%) with TC＜1%, 12 (6%) with TC among 1-25%. These results showed TC expression in all patients were less than 25%, suggesting that ovarian cancer may be an immunologically cold tumor. Conclusions: This is firstly showing the HRD and PD-L1 status in Asian OC patients. The results showed all the PSR patients could benefit from Olaparib treatment, regardless of HRD status. Meanwhile the numerically different mPFS observed across different HRD status subgroups also indicated potential clinical utility of locally developed HRD assay. Clinical trial information: NCT03534453.

**Calculated based on the number of patients in each subgroup. mPFS, median progression-free survival.