Incorporating liquid biopsies into treatment decision-making: obstacles and possibilities

•Liquid biopsies provide unique real-time data on cancer, but clinical use is limited.•Current data on liquid biopsies is dominated by proof-of-concept studies.•Harmonization of (pre-)analytical conditions is essential for clinical validity.•Performing interventional trials is essential for clinical utility. Circulating tumor cells (CTCs) and cell-free DNA (cfDNA) together with newer emerging liquid biopsies have a unique potential to deal with key issues in oncology. For example, they can be used to assess prognosis, direct treatment with certain kinds of drug, or provide information about response to treatment. However, despite an overflow of literature on the subject, clinical implementation of these liquid biopsies has been scarce. This is mainly because there is a lack of preanalytical standardization, multiple different techniques or platforms are being used, and a lack of prospective studies investigating a meaningful clinical question are performed. Here, we provide an overview of the current state of liquid biopsies and make suggestions for how liquid biopsies can reach the tipping point.