The concept of a “liquid biopsy” is that one could use blood (or other body fluids) to monitor any tumour material present in the systemic circulation. This could be either circulating tumour cells (CTCs), circulating cell free DNA (cfDNA) or specifically circulating tumour DNA (ctDNA). This has several potential uses:

· Analysis to look for a specific mutation to allow use of a therapy targeted against that mutation, especially where it is not possible to obtain a tissue sample

· Monitoring of tumour burden or response to treatment

· Confirmation of the presence or absence of small amounts of residual cancer in patients being considered for adjuvant systemic therapies

· Screening for cancer at a population level