Niraparib (PARP inhibitor) is approved in advanced ovarian cancer (OC) as maintenance therapy in the first line and recurrent platinum-sensitive settings. The MONITOR-UK study was designed to report real-world niraparib experience in UK clinical practice. In this national, multi-centre, observational study (NCT04295577), patients with newly diagnosed or recurrent OC treated with maintenance niraparib were enrolled. The primary endpoint is the incidence of grade ≥3 treatment emergent adverse events (TEAEs). Secondary endpoints include PFS and quality of life. Recruitment is ongoing (n=375 planned). We report an initial, descriptive analysis of subjects enrolled with at least 6 months (mo) follow up. Between 12/2019 and 8/2023, 319 eligible patients were enrolled from 14 centres; median age 68 years (IQR 59-74); 166/319 (52%) first line (139/166 (84%) prospective); 153/319 (48%) recurrent OC (110/153 (72%) prospective); 300mg initial dose 24%. Median follow-up 17.3 mo (IQR 8.7 - 27.8). Among first line patients, 111/166 (67%) stage III at initial diagnosis; 59/166 (36%) neoadjuvant chemotherapy; 126/166 (76%) cytoreductive surgery; 103/126 (82%) no residual disease. 106 (33%) patients experienced a grade ≥3 TEAE: hypertension (n=44, 14%), anaemia (n=27, 8%), low neutrophil (n=20, 6%) and low platelet count (n=20, 6%). Adverse events of special interest included secondary cancer diagnosis (n=6), pneumonitis (n=2), AML (n=1) and MDS (n=1). Discontinuation rate due to TEAEs was 5%. 47% patients had dose reductions. In the first line, median PFS for all-comers was 12.5 mo (95% CI, 9.7 - 15.8); median PFS for stage III without residual disease 14.6 mo (95% CI, 11.3 - 17.3) and 8.5 mo (95% CI, 5.6 - 10.8) for stage III with residual disease. In patients with recurrent disease, the PFS was 15.4 (95% CI, 8.5 - 40.9) and 7.1 (95% CI, 5.4 - 8.5) mo in BRCA-mutated (n=17, 11%) and all-comers, respectively. In this real-world, ongoing, observational study, which included first line patients without residual disease, the occurrence of treatment-related adverse events graded ≥3 reported is lower than reported in phase III clinical trials. Clinical outcomes and biomarker status will be updated.

52P MONITOR-UK: An initial analysis of a multi-centre, observational study of maintenance niraparib in ovarian cancer