Exosomes: A Source for New and Old Biomarkers in Cancer

SIMPLE SUMMARY: The follow-up of patients with tumors needs new or at least more reliable biomarkers to avoid invasive approaches. Unfortunately, the existing biomarkers too often have generated more problems than having proven to be sufficiently helpful for the clinical oncologists. Very recently, translational research has focused on extracellular vesicles, with size ranging between micro to nano as potential sources of new tumor biomarkers. In particular, nanovesicles (called exosomes) that are variably released from virtually all cells, have shown to be a potential source of new tumor biomarkers but also a preferential delivery system for well-known biomarkers, such as PSA and CEA. The clinical data supporting this new research area are, unfortunately, very few, but the existing reports are very encouraging. We review and discuss the existing literature supporting a key role of exosomes as a source of tumor biomarkers, together with some unexpected discoveries. ABSTRACT: Clinical oncology needs reliable tumor biomarkers to allow a follow-up of tumor patients who do not necessarily need invasive approaches. To date, the existing biomarkers are not sufficiently reliable, and many of them have generated more problems than facilitating the commitment of clinical oncologists. Over the last decades, a broad family of extracellular vesicles, with size ranging between micro to nano, has been raised as a new hope for potential sources of new tumor biomarkers. However, while knowledge in the field is increasing, we do not currently have definitive information allowing a clinical use of extracellular vesicles in cancer clinics. Recent evidence provides new perspective in clinical oncology, based on data showing that circulating nanovesicles called exosomes may represent a valuable source of tumor biomarkers. In this review, we discuss the existing clinical data supporting a key role of exosomes as a source of tumor biomarkers, including proteins and miRNAs, but also discuss the importance of the expression of known tumor biomarkers when expressed on exosomes.