Crizotinib is a potent inhibitor of ALK and is approved for the treatment of advanced ALK+ NSCLC patients. This is an example of personalized medicine, where patients are selected for treatment based upon a molecular assay, and are provided a specific therapy (crizotinib) for their disease. The pharmacoeconomic impact of using genetic information in early treatment decisions in NSCLC has not been determined. Despite the benefits of crizotinib, some patients do not respond to treatment and most patients will eventually develop resistance. To date, it is unclear why some rare patients do not respond to treatment and the resistance mechanisms of crizotinib have not been fully elucidated.