Project Summary The use of genotype directed precision therapies, including epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitors (TKIs) in EGFR mutant or ALK rearranged non- small cell lung cancer (NSCLC), respectively, is associated with improvements in both response rate (RR) and progression free survival (PFS) compared to chemotherapy. However, the PFS improvements are typically only counted in months rather than years. Despite the development of next generation TKIs that can overcome specific resistance mechanisms, it is very unlikely that any patient will be cured from their advanced lung cancer using sequential single agent treatment. It is more than likely that significant improvements in patient outcomes using precision therapies will only occur through the use of combination therapies. In the current proposal we integrate pre-clinical in vitro and in vivo studies, with clinical trials and serial non-invasive analyses of patient's tumors using cell free DNA to develop combination therapies. We focus primarily on EGFR mutant lung cancer as this is the largest subset of NSCLC patients treated with precision therapies and as there is a desperate need to developing more effective therapies for EGFR mutant patients. The approaches to developing combination therapies include a.) dual targeting of EGFR, b.) vertical pathway inhibition (combining EGFR inhibition with downstream signaling inhibition) and c.) parallel pathway inhibition (combining EGFR inhibition with other signaling pathways). Our strategy will focus on improving therapies for EGFR inhibitor naïve cancers, as such cancers are genetically the most homogeneous, and where improving treatment approaches will likely translates into the greatest clinical benefit by delaying and/or preventing the emergence of acquired drug resistance. Our preclinical studies provide the rationale for the combination clinical studies and their success (or lack thereof) and toxicity in the clinic will inform about additional preclinical approaches to further refine treatments. Through this iterative process, our goal is to make significant improvements in the outcome of EGFR mutant and other lung cancer patients treated with genotyped directed therapies.