A wealth of recent advances in liquid biopsies have shown them to be clinically useful for tumour biomarker detection in known tumour types; for example, blood-based EGFR mutation testing in NSCLC is used within the clinic to detect circulating tumour DNA (ctDNA) harbouring common EGFR mutations that predict response/resistance to EGFR inhibitors.81 There are, however, very few studies investigating the role of liquid biopsies in CUP (summarised in Table 3). Here, EGFR is linked to neoplasm.