Deletion of PARP1 using CRISPR/Cas9 gene editing tools in two ovarian cancer cells (one with BRCA1 mutation and one with BRCA1 promoter methylation) shows >90% reduction of PARP1 expression in BRCA1 mutant and promoter methylated cells as measured by immunofluorescence and western blot analysis. The gene discussed is PARP1; the disease is ovarian carcinoma.