To investigate whether heterozygous and homozygous BRCA1 promoter methylation correlated with PARPi response in clinical samples, we used quantitative MS-ddPCR to analyze the archival and pre-treatment (study-entry) tumor biopsies from 21 patients who were identified to have BRCA1-methylated HGSOC from the cohort of 204 patients treated on the ARIEL2 Part 1 single-agent rucaparib trial32 (detail provided in methods, Table 2, Supplementary Data 5). The gene discussed is BRCA1; the disease is neoplasm.