Circular RNAs (circRNAs), characteristic of covalently closed loops generated by back-splicing, are a subclass of single-stranded RNA molecules. Owing to the circular structures, circRNAs are protected from exonuclease-induced degradation, which makes them more stable compared with linear RNAs. With the development of high-throughput sequencing technology and bioinformatics, the roles of circRNAs in a variety of physiological and pathophysiological processes have been increasingly revealed. Although the functions of most circRNAs remain largely elusive, accumulating studies have identified them as microRNA(miRNA) sponges, protein regulators, transcriptional regulators, protein templates, and so forth. In this review, we briefly describe the biogenesis of circRNAs and provide an overview on their functions in cancers, including miRNA sponges, protein regulators, transcriptional regulators, protein templates. Furthermore, we discuss the potential application of circRNAs as biomarkers and give insight into future perspectives.

环状RNA（circRNA）是通过反向剪接产生的共价闭环的特征，是单链RNA分子的一个子类。由于具有环状结构，因此可以保护circRNA免受核酸外切酶诱导的降解，这使其与线性RNA相比更加稳定。随着高通量测序技术和生物信息学的发展，circRNA在各种生理和病理生理过程中的作用日益被揭示。尽管大多数circRNA的功能仍然难以捉摸，但越来越多的研究已将其识别为microRNA（miRNA）海绵，蛋白质调节剂，转录调节剂，蛋白质模板等。在这篇综述中，我们简要介绍了circRNA的生物发生，并概述了其在癌症中的功能，包括miRNA海绵，蛋白质调节剂，转录调节剂，蛋白质模板。此外，我们讨论了circRNAs作为生物标志物的潜在应用，并提供了对未来观点的见识。