Exosomes as a liquid biopsy for lung cancer

In lung cancer and other malignancies, the so-called "liquid biopsy" is quickly moving into clinical practice. Its full potential has not yet been fully identified, but the "liquid biopsy" is no longer a promise but has become a reality that allows for better treatment selection and monitoring of lung cancer. This emerging field has significant potential to make up for the limitations of the traditional tissue-derived biomaterials. Exosomes are spherical nano-sized vesicles with a diameter of 40-100 nm and a density of 1.13-1.19 g/ml. In both physiological and pathological conditions, exosomes can be released by different cell types, including immune cells, stem cells and tumor cells. These small molecules may serve as promising biomarkers in lung cancer "liquid biopsy" as they can be easily obtained from most body fluids. In addition, the lipid bilayer of exosomes allows for stable cargoes which are relatively hard to degrade. Furthermore, the composition of exosomes reflects that of their parental cells, suggesting that exosomes are potential surrogates of the original cells and, therefore, are useful for understanding cell biology. Previous studies have demonstrated that exosomes play important roles in cell-to-cell communication. Moreover, tumor-derived exosomes are evolved in tumor-specific biological process, including tumor proliferation and progression. Recently, a growing number of studies has focused on exosomal cargo and their use in lung cancer genesis and progression. In addition, their utility as lung cancer diagnostic, prognostic and predictive biomarkers have also been studied. The current review primarily summaries lung cancer-related exosomal biomarkers that have recently been identified and discusses their potential in clinical practice.