VIEWPOINT

examine gene expression for the elucidation of biological mechanisms. Gene-expression pro-files are now being used as classifiers of patients’ prognosis and response to therapy.1 The development of traditional prognostic and diagnostic biomarkers has been largely disap-pointing. The extensive literature on this topic is often contradictory and relatively few oncologic biomarkers have been adopted in clinical prac-tice.2,3 One reason is that biomarker studies are generally performed retrospectively using hetero-geneous specimens with no prespecified hypoth-eses. Generally, this approach does not provide an appropriate context for reliable development of a therapeutically relevant classifier. Many stud