Rucaparib in patients with BAP1-negative or BRCA1-negative mesothelioma met the prespecified criteria for success, showing promising activity with manageable toxicity...Ten (38%) of 26 patients were BAP1 negative and BRCA1 negative, 23 patients (89%) were BAP1 negative, and 13 patients (50%) were BRCA1 negative...Disease control rate at 12 weeks was 58% (95% CI 37–77; 15 of 26 patients), and at 24 weeks was 23% (9–44; six of 26 patients).