Ovarian cancers are among the most deadly cancers for women. We need better drugs to treat women with ovarian cancer. Recent studies show that certain ovarian cancers have mutations in unique genes. For example, 60% of epithelial ovarian cancers (EOC) have mutations in the ARID1A gene. This is an important clue to understand EOC and how to treat it. ARID1A mutation forces these cancers to rely on the related protein ARID1B. ARID1B is thus an attractive target for drug discovery. ARID1A and ARID1B are proteins that control gene transcription. However, we do not why ARID1B is vital for ovarian cancers. Using new methods, we will find the genes that ARID1B controls in EOC. We will design a system to eliminate ARID1B in EOC to test if ARID1B is a good drug target. Cancers can often find ways to escape our drugs and come back. We will find loopholes that ovarian cancers use to escape ARID1B elimination. Our goal is to find new strategies to treat women with ARID1A mutant EOC.