Presence and prospects of exosomal circRNAs in cancer (Review).

Exosomes are nanoscale extracellular vesicles secreted by parent cells and they are present in most bodily fluids, are able to carry active substances through intercellular transport and mediate communication between different cells, in particular those active in cancer. Circular RNAs (circRNAs) are novel noncoding RNAs expressed in most eukaryotic cells and are involved in various physiological and pathological processes, particularly in the occurrence and progression of cancer. Numerous studies have indicated a close relationship between circRNAs and exosomes. Exosomal circRNAs (exo‑circRNAs) are a type of circRNA enriched in exosomes that may participate in the progression of cancer. Based on this, exo‑circRNAs may have an important role in malignant behavioral manifestations of cancer and hold great promise in the diagnosis and treatment of cancer. The present review gives an introduction to the origin and functions of exosomes and circRNAs and elaborates on the mechanisms of exo‑circRNAs in cancer progression. The biological functions of exo‑circRNAs in tumorigenesis, development and drug resistance, as well as their role as predictive biomarkers, were discussed.