ABSTRACT We aimed to develop the mutational signature‐based BioMarker (MSBM) to define homologous recombination deficiency (HRD) in newly diagnosed, advanced ovarian cancer and overcome limitations of genomic scar‐based assays. We conducted a phase 2 trial (MSBM‐OL) to evaluate the efficacy of olaparib maintenance monotherapy and to validate MSBM as a novel HRD biomarker. The MSBM was designed to integrate three whole‐exome sequencing‐derived features without using genomic scars: tumor‐ BRCA mutation status, Mutational Signature 3 similarity score > 0.5, or score > 0.25 without CCNE1 amplification. Among 170 patients with stage IIIC/IV high‐grade ovarian carcinoma, 58 HRD‐positive patients responding to platinum‐doublet chemotherapy (without bevacizumab) were enrolled. Thirty‐two were randomized 2:1 to olaparib or placebo, and 26 enrolled after switching to a single‐arm study. The primary endpoint was progression‐free survival (PFS), evaluated against a predefined median of 9 months. Of 170 patients, 169 were evaluable for HRD (99.5%) and 123 (72.4%) were HRD‐positive by MSBM, including 21.1% with tumor‐ BRCA mutations. The olaparib arm ( n = 45) showed a median PFS of 22.3 months, significantly exceeding the 9‐month threshold ( p < 0.001), meeting the primary endpoint. The placebo arm ( n = 11) with a median PFS of 16.7 months was not powered for comparison. Grade ≥ 3 adverse events included anemia (25.5%) and neutropenia (12.8%). In a subset ( n = 16), MSBM showed 81% concordance with myChoice CDx and correlated with genomic instability scores ( R = 0.63). MSBM enables robust HRD evaluation from a whole‐exome sequencing assay. Olaparib monotherapy demonstrated clinical benefit for first‐line maintenance in HRD‐positive ovarian cancer without bevacizumab.
Oda et al. (Sun,) studied this question.