LAUSR

5551 Background: In SOLO1 (NCT01844986), maintenance olaparib resulted in a significant improvement in progression-free survival (PFS) for newly diagnosed, BRCA1- and/or BRCA2-mutated, advanced ovarian cancer pts compared with placebo (HR 0.30, 95% CI 0.23–0.41; median not reached vs 13.8 months; Moore et al. N Engl J Med 2018). We investigated PFS in SOLO1 for the subgroups of pts with BRCA1 mutations ( BRCA1m) or BRCA2 mutations ( BRCA2m). Methods: All pts were in clinical complete or partial response to platinum-based chemotherapy and were randomized to maintenance olaparib (300 mg twice daily; tablets) or placebo. After 2 years, pts with no evidence of disease discontinued study treatment, but pts with evidence of disease could continue study treatment. PFS by BRCAm was a predefined analysis. BRCAm were identified by central germline (Myriad or BGI) or local testing; Foundation Medicine testing confirmed tumor BRCAm. Results: Median follow-up for PFS was ~41 months in the olaparib and placebo arms. Of 391 randomized pts, 282 had BRCA1m (72%), 106 had BRCA2m (27%) and three (1%) had both (Table). Two pts in the olaparib arm had somatic BRCAm (one BRCA1m, one BRCA2m); all others had germline BRCAm. At the primary data cut-off, 155 pts in the BRCA1-mutated group (55%), 43 in the BRCA2-mutated group (41%) and none in the BRCA1/2 -mutated group had disease progression. The percentage of BRCA1-mutated pts who received olaparib and were progression-free at 1, 2 and 3 years was 86%, 69% and 53% (vs 52%, 36% and 26% receiving placebo) and for BRCA2-mutated pts was 92%, 85% and 80% (vs 50%, 32% and 29%, respectively). Conclusions: Significant PFS benefit with olaparib versus placebo was demonstrated for all pts, regardless of whether they had BRCA1m or BRCA2m. Statistical tests were not used to compare BRCA1- and BRCA2-mutated pts, but those with BRCA2m appeared to receive greater benefit from maintenance olaparib than those with BRCA1m. Clinical trial information: NCT01844986. [Table: see text]