Circular RNA in Exosomes.

Circular RNAs (circRNAs) are a novel family of non-coding endogenous RNAs discovered in all eukaryotic cells and generated through a particular mechanism of alternative splicing called "back-splicing". These molecules show multiple functions, by acting as modulators of gene and miRNA expression, and may have a role in several biological processes, such as cell proliferation and invasion with, tumour development and progression, and in several mechanisms underlying other diseases. Their presence has been shown to be abundant in several body fluids such as blood and saliva. Based on their biogenesis mechanism, circRNAs may be categorized into five classes: exonic circRNAs, intronic circRNAs, antisense circRNAs, sense overlapping circRNAs and intergenic circRNAs. Recently, the presence of circRNAs, in addition to that of miRNAs and long non-coding RNAs, has been detected also in small extracellular vesicles called exosomes. Investigating the presence and expression levels of serum exosomal circRNAs could allow us, in future, to discriminate cancer patients from healthy individuals, identifying new potential exosome-based cancer biomarkers.In this chapter, we briefly will describe the major features and functions of exosomal circRNAs, discussing their potential role as molecular biomarkers for diagnosis, prognosis and monitoring of complex diseases, including cancer.