Combination chemotherapies have been a mainstay in the treatment of disseminated malignancies for almost 60 years, yet even successful regimens fail to cure many patients. Because these regimens were designed empirically, the precise mechanisms of single component drugs, as well as aggregate mechanisms of combination regimens, are poorly understood. The Hemann lab has combined tractable loss of function genetic tools complementary informatics tools to examine front-line cancer drugs. By using this approach, they have been able to identify unexpected mechanisms of action of very commonly used chemotherapies – information that is critically need to guide the best use of these compounds. Additionally, they have developed approaches to predict combination drug mechanisms of action that are independent of biochemical mechanism and have implications for biomarker discovery as well as for the development of regimens with defined genetic dependencies. Finally, extensions of this technology have provided a basis for studying tumor heterogeneity, tumor evolution and the emergence of resistant clones from heterogeneous tumor populations following therapy.