Keith Kerr, MB, ChB, FRCPath, FRCPE from the University of Aberdeen, Aberdeen, Scotland, discusses the development of liquid biopsies at the European Cancer Congress of the European Cancer Organisation (ECCO) 2017 in Amsterdam, Netherlands. For some biomarker and DNA based tests, instead of taking a tumor biopsy, a liquid biopsy might be a viable alternative. A liquid biopsy involves testing for biomarkers and cell-free DNA in the blood, which is less invasive, and could be useful for individuals who are not fit enough for biopsy. It does, however, have disadvantages. For example, the copy numbers of some mutated genes in cell-free DNA are very low. Highly sensitive techniques would need to be developed for these genes, which may in turn lead to an increased number of false positives. This is very promising for a large group of patients, despite not being appropriate for all.