Tracking tumor resistance using 'liquid biopsies'

Cancers are known to evolve in response to therapy, which may result in drug resistance. However, following this process in patients is challenging, as repeated biopsies of tumor tissue involves invasive procedures and tumor heterogeneity confounds interpretation of analyses. A recent study by Murtaza et al. 1 describes an approach to trace the genomic evolution of tumors in response to therapy by sampling circulating cell-free tumor DNA (ctDNA) from patient plasma at different time points during treatment. This strategy allowed the authors to detect mutations associated with therapy resistance. We asked three experts to comment on this study and its implications for studying and treating tumors in the clinic.