The liquid biopsy: towards standardisation in preparation for prime time

The liquid biopsy holds potential as a more cost-effective, easier, and less invasive method for diagnosing and monitoring cancer, as well as predicting response, than currently available approaches (such as tissue biopsies or imaging scans). Circulating tumour cells (CTCs) and circulating cell-free DNA (cfDNA) are currently the most intensely investigated analytes, with some tests already approved in clinical practice (eg, the Cobas EGFR mutation test v2, Roche, Burgess Hill, UK). Despite the potential of the liquid biopsy for managing patient therapy, no widely accepted consensus has been reached regarding pre-analytical blood sample handling and technologies used for extracting cfDNA and isolating CTCs, or optimal workflows for their molecular analyses, all of which are required before liquid biopsies can become routinely used in the clinic. In this Comment, we discuss the current status of liquid biopsy testing in patients with solid tumours, and the variation in blood sample handling and isolation or extraction methods, focusing on cfDNA and CTCs.