This recent experience with these targeted agents in solid tumors, while still promising, has yielded relatively modest results.7-11 Notably, however, retrospective analyses of clinical trials are consistently revealing that differences in treatment effect between subgroups of patients can be associated with specific molecular profiles.12-18 These findings suggest the potential for a more rational approach to trial design that would use patient and tumor characteristics to select patients for therapy, thus enriching the population of responders.