Circular (circ)RNAs, naturally formed endogenous non-coding RNAs, have received 
extensive attention in recent years due to their special loop structures and 
specific function. circRNAs are formed with covalently closed continuous loops 
and are mainly generated by back-splicing processes or lariat introns from exons 
and/or introns. Usually, circRNAs are stable, abundant, and evolutionarily 
conserved in the cytoplasm. circRNAs often exhibit abnormal expression in 
different diseases, notably in human cancers, and the presence of abundant 
circRNAs in serum, saliva and exosomes renders them potential diagnostic or 
predictive biomarkers for diseases, including multiple types of cancer. 
Presently, certain circRNAs have been reported to function as microRNA sponges 
and RNA-binding protein sponges to regulate downstream gene transcription, which 
suggests a potential for circRNAs in cancer diagnosis, prognosis and clinical 
therapy. The present study assessed the latest advances in the study of circRNAs 
in cancer, summarized the functions of circRNAs in different types of cancer, 
highlighted the competing endogenous RNA function of circRNAs in the occurrence 
and development of human malignancies, and provided evidence for the future 
application of circRNAs in the diagnosis, prognosis and treatment of multiple 
types of cancer.