Blood-Based Companion Diagnostics
Since the seminal reports of the utility of circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs) in evaluating a cancer patient’s response to therapy (1,2), the field of blood-based nucleic acid testing (also referred to as “liquid biopsies”) has intensified and accelerated. A recent, comprehensive review of ctDNA and CTCs (3) summarizes research and technical advances in both areas. The goal ofthis editorial is to discuss how these technologies can be used in the development of non-invasive companion diagnostics that can be used in patient stratification and in monitoring of drug response and of drug resistance.These blood-based diagnostics can obviate the need for tissue biopsy, providing an attractive solution when tissue is limiting or in instances where biopsies are not routinely performed, and may provide a more accurate representation of tumor heterogeneity and evolution. However, there are several technical, regulatory and commercial issues that must be considered when developing this next generation of companion diagnostics.