Figure 2.

Strong points and caveats of plasma-based (left) and CSF-based (right) liquid biopsy of cfDNA. Both plasma and CSF can be precious sources of genetic material shed by brain tumours in bodily fluids. On one hand, venous blood sampling is less invasive than CSF withdrawal, and can be easily repeated during clinical follow-up, and namely during routine outpatient visits. On the other hand, CSF generally contains larger amounts of tumour-derived genetic material and lesser amounts of genetic material released from normal cells, resulting in higher rates of mutation detection. Moreover, the total amount of cfDNA in plasma may also transiently increase due to intervening conditions (e.g. venous thromboembolism,⁹⁰ inflammation,⁹¹ sepsis,^91,92 focal epilepsy⁹⁴), which should be accounted for during result interpretation. cfDNA = cell-free DNA; CNVs = copy number variations; CTCs = circulating tumour cells; EVs = extracellular vesicles; VS = ventricular shunt. Created with Biorender.com.