Immune checkpoint blockade has shown great potential in oncology. However, only a fraction of patients benefits from this therapy. Furthermore, severe immune-related adverse events occur in a part of the patients, and financial toxicity cannot be underestimated. It is therefore important to develop predictive biomarkers to differentiate responders from non-responders. Tumour tissue samples offer a large amount of information as anti-tumour immunity is regulated through multiple factors in the tumour microenvironment. The potential of tumour-infiltrating immune cells was investigated to predict response to therapy and survival. In contrast to tissue biopsies, liquid biopsies allow for collection in a less invasive manner, allow for repetitive sampling during therapy, and offer information on all cancer cells in the tumour as well as metastases at distinct locations in the body. Extracellular vesicles (EVs) present in the circulation are a spatiotemporal fingerprint of the cell of origin. Therefore, EV-derived information has the potential to be used for diagnosis, prognosis, treatment selection and evaluating treatment response. However, the clinical application of EVs is currently hampered by a lack of sensitive, high-throughput and fast EV analysis techniques.

(BELG J MED ONCOL 2023;17(2):63–5)