Background: In the Phase II Study 19 trial (NCT00753545; Ledermann et al Lancet Oncol 2014), maintenance olaparib improved progression-free survival (PFS) vs placebo in PSR OC pts, including non-BRCAm pts. A significant PFS benefit was also seen with maintenance olaparib vs placebo in gBRCAm PSR OC pts in the Phase III SOLO2 trial (NCT01874353; Pujade-Lauraine et alLancet Oncol 2017). To investigate olaparib maintenance monotherapy in non-gBRCAm PSR OC pts who had received ≥2 prior lines of platinum-based chemotherapy (PBC), we performed the Phase IIIb, single-arm, OPINION study (NCT03402841). Methods: Pts had high-grade serous or endometrioid OC and were in complete response (CR) or partial response (PR) to PBC. Pts received maintenance olaparib (tablets; 300 mg bid) until disease progression or unacceptable toxicity. The primary endpoint was investigator-assessed PFS (modified RECIST v1.1). Secondary endpoints included PFS by homologous recombination deficiency (HRD) and somatic BRCA mutation (sBRCAm) status determined by central Myriad tumor and germline testing; and time to first subsequent treatment (TFST). The primary analysis was planned for 18 months (mo) after the last patient was enrolled. Results: 279 pts were enrolled from 17 countries (mean age: 64 years); 253 pts (90.7%) were confirmed non-gBRCAm. At data cut-off (Oct 2, 2020), median PFS was 9.2 mo (95% CI 7.6–10.9), with 210 PFS events (75.3% maturity). 65.3%, 38.5% and 24.3% of pts were progression-free (PF) at 6, 12 and 18 mo, respectively. The Table shows PFS in key subgroups. Median TFST was 13.9 mo (95% CI 11.5–16.4). Median exposure to olaparib was 9.4 mo (range 0.0–31.9). Grade ≥3 treatment-emergent adverse events (TEAEs) occurred in 29.0% of pts and serious TEAEs in 19.7% of pts. TEAEs led to dose interruption, dose reduction and treatment discontinuation in 47.0%, 22.6% and 7.5% of pts, respectively. Conclusions: Our findings support the use of olaparib maintenance therapy in non-gBRCAm PSR OC pts, consistent with our interim analysis and previous trials in this setting. Clinical trial information: NCT03402841

*Genomic instability score ≥42 NE, not evaluable; NED, no evidence of disease.