Overall response rate was 8.3% and CBR was 62.5% among the entire cohort. Two of five patients with tumor harboring ATM mutation achieved CR or SD ongoing at 24+ months, respectively (CBR 40%). Of seven patients with PARP inhibitor-resistant HGSOC, one achieved PR (-90%) and five had SD ranging 16-72 weeks (CBR 86%). Olaparib with ceralasertib demonstrated preliminary activity in ATM-mutated tumors and in PARP inhibitor-resistant BRCA1/2-mutated HGSOC.