Real world data of maintenance treatment in homologous recombination (HR)–proficient HGSOC.

e17610 Background: Poly (ADP)-ribose polymerase (PARP) inhibitors with or without bevacizumab have increased 5-year overall survival to over 50% in homologous recombination (HR)-deficient high-grade serous ovarian carcinoma (HGSOC). However, the optimal maintenance treatment for patients with FIGO stage III/IV HR-proficient HGSOC remains uncertain. ICON7 and GOG-218 studies showed that bevacizumab confers overall survival (OS) advantage in high-risk patients with stage IV disease, inoperable or suboptimally debulked stage III disease. On the other hand, PRIMA/ENGOT-OV26 trial showed no OS benefit in stage III/IV HR-proficient patients at 5-year follow up. Methods: We retrospectively evaluated 179 patients with FIGO stage III/IV HGSOC that received treatment in the Oncology Department of Alexandra University Hospital between 01/2019 and 08/2024. All patients underwent HRD testing with either Myriad myChoice NGS panel CDx or AmoyDx HRD Focus NGS Panel/ OncoScan as part of the nationwide patient support program from the Hellenic Society of Medical Oncology (HeSMO). Results: Median age was 61.3 years (SD±11.3). 121 patients (67.6%) had FIGO stage III disease while 58 patients (32.4%) had stage IV. 71 patients (39.7%) were HRD-, 64 patients (35.8%) were HR+/BRCAwt and 44 (24.5%) patients were HRD+/BRCAmut. Median progression-free survival (PFS) was 13.1 for the HRD- group, 26.9 for the HRD+/BRCAwt population and 31.6 for the HRD+/BRCAmut group. In the HRD- population, 24 (33.8%) patients received maintenance treatment with bevacizumab while 31 (43.7%) patients received maintenance treatment with PARP inhibitor niraparib. There was a statistically significant difference in PFS between those treated with niraparib compared to bevacizumab (χ 2 = 4.483, p= 0.034). Median PFS was 15.3 months for those treated with niraparib compared to 12.2 months for those treated with bevacizumab maintenance. However, Cox regression analysis revealed that first line maintenance treatment was not significantly associated with PFS (HR= 0.68, 95%CI: 0.33-1.41, p= 0.302 ) after adjusting for age, performance status, surgery and disease stage. Conclusions: In HR-proficient patients,first line maintenance treatment was not significantly associated with PFS in multivariate analysis. Maintenance treatment types according to HRD and BRCA mutation status. HRD- HRD+/BRCAwt HRD+/BRCAmut No maintenance 13 (18.3%) 8 (12.5%) 3 (6.8%) Avastin 24 (33.8%) 2 (3.1%_ 1 (2.3%) Bevacizumab + PARPi 3 (4.2%) 37 (57.8%) 14 (31.8) PARPi 31 (43.7%) 17 (26.6%) 26 (59.1%) PARPi: PARP inhibitor.