Epigenetic aberrations are key drivers of multiple myeloma (MM), yet targeted therapies exploiting epigenetic alterations have not been established. By integrating clinical and molecular MM patient data sets with an unbiased genetic in vivoscreen, we identified KAT8 regulatory NSL complex subunit 2 (KANSL2) as a histone posttranslational modification (PTM)-associated candidate oncogene. High expression of KANSL2 was associated with adverse prognosis in MM patients. Genetic gain and loss of function models identified a protective role of KANSL2 towards genotoxic stress. By transcriptomics, proteomics and quantitative acetylome profiling, we identified a KANSL2-dependent specific molecular program targetable by acetylation-related modifiers. High KANSL2 levels increased sensitivity to the histone deacetylase (HDAC) inhibitor panobinostat and bromodomain and extra-terminal motif (BET) inhibitor OTX-015 and their combination. Ex vivo drug response profiling revealed that high KANSL2 expression enhances sensitivity to HDAC and BET inhibitors in primary MM patient samples. Collectively, these findings position KANSL2 as a mediator of chemotherapy resistance and actionable biomarker for response to epigenetic regulators.