Developing precision medicine in a global world.

Advances in understanding the biology of cancer, as well as advances in diagnostic technologies, such as the advent of affordable high-resolution DNA sequencing, have had a major impact on the approach to identification of specific alterations in a given patient's cancer that could be used as a basis for treatment selection, and hence the development of companion diagnostics. Although there are now several examples of successful development of companion diagnostics that allow identification of patients who will achieve the greatest benefit from a new therapeutic, the path to coapproval of a diagnostic test along with a new therapeutic is complex and often inefficient. This review and the accompanying articles examine the current state of companion diagnostic development in the United States and Europe from academic, industry, regulatory, and economic perspectives. See all articles in this CCR Focus section, "The Precision Medicine Conundrum: Approaches to Companion Diagnostic Co-development."