Circular RNAs and exosomes in cancer: a mysterious connection

Circular RNAs (CircRNAs) are a type of non-coding RNAs (NcRNAs) with a closed annular structure. Until next-generation sequencing (NGS) is developed, the misunderstanding of circRNAs 'splicing error' has changed, and the mysterious veil of circRNAs has been revealed. NGS provides an approach to investigate circRNAs. Many scholars point out that circRNAs may play an important role in many diseases, especially cancer. At the same time, exosomes, as a kind of extracellular vesicles loaded with many contents, are a hotspot in recent years. They can act as 'messengers' between cells, especially in cancer. Lately, it is interesting circRNAs are enriched and stable in exosomes, also called exo-circRNAs, and there have been several articles on circRNAs associated with exosomes. In this review, we summarize the characteristics of circRNAs, especially its main functions. Then, we briefly introduce exosomes and their function in cancer. Finally, the known relation between circRNAs and exosomes is discussed. With further researches, exo-circRNAs may be a novel pathway for cancer diagnosis and targeted therapy.