This thesis bridges the gap between solid tissue and liquid biopsies and demonstrates the utility of circulating tumour (ct)DNA detection in an academic hospital. We show that routine mutation analysis of ctDNA is technically feasible and can inform clinical decisions in diverse subsets of cancer patients. However, the utility of ctDNA detection is currently hindered by poorly understood biological variables. Until these gaps in our knowledge are filled, ctDNA detection will be mostly restricted to a test of last resort or to support solid tissue biopsies.