Abstract Epigenetic dysregulation is an emerging hallmark of cancers, and the identification of recurrent somatic mutations in chromatin regulators implies a causal role for altered chromatin states in tumorigenesis. As the majority of epigenetic mutations are inactivating and thus do not present directly druggable targets, we reasoned that these mutations may alter the epigenomic state of cancer cells and thereby expose novel epigenetic vulnerabilities. To systematically search for epigenetic synthetic lethal interactions, we performed a deep coverage pooled shRNA screen across a large collection of cancer cell lines using a library targeting a diverse set of epigenetic regulators. Strikingly, this unbiased screen revealed that silencing of the SWI/SNF ATPase subunit BRM/SMARCA2, selectively inhibits the proliferation of BRG1-deficient cancer cells. The mammalian SWI/SNF complexes (mSWI/SNF) regulate chromatin structure through ATP-dependent nucleosome remodeling. Recent cancer genome studies have revealed a significant frequency of mutations in several components of the mSWI/SNF complexes including loss of the catalytic subunit BRG1 in non-small cell lung cancers. Our studies reveal that BRM knockdown selectively induced cell cycle arrest in BRG1-mutant cancer cells and significantly impaired the growth of BRG1-mutant lung tumor xenografts. BRM is the paralog of BRG1, suggesting a model in which mSWI/SNF mutations lead to a hypomorphic complex that promotes tumorigenesis but cannot tolerate complete inactivation. Therefore, our studies present BRM as an attractive therapeutic target in BRG1-mutant cancers. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):PR06. Citation Format: Zainab Jagani, Gregory Hoffman, Rami Rahal, Frank Buxton, Gregory McAllister, Kay Xiang, Elizabeth Frias, Janina Huber, Alicia Lindeman, Dongshu Chen, Linda Bagdasarian, Rodrigo Romero, Nadire Ramadan, Tanushree Phadke, Kristy Haas, Mariela Jaskelioff, Boris Wilson, Matthew Meyer, Margaret E. McLaughlin, Charles WM Roberts, Vic Myer, Jeff Porter, Nicholas Keen, Craig Mickanin, Frank Stegmeier. A functional screen of the epigenome identifies BRM/SMARCA2 as a critical synthetic lethal target in BRG1-deficient cancers. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr PR06.