Circular RNA(circRNA)is a novel type of endogenous non-coding RNA.Most circRNAs 
act as microRNA(miRNA)sponges to regulate the expression of functional genes.In 
addition,some circRNAs can be translated and interact with RNA-binding proteins 
to perform biological functions.The expression of circRNAs is prevalent in 
tissues and body fluids,and their abnormal expression is related to tumor 
progression.circRNAs are stable even under the treatment of RNase R because of 
their circular conformation.As circRNAs have construct stability,wide 
variety,specific regulation of tumor progression and high expression in body 
fluids,it is potential for circRNAs to serve as candidate diagnostic,prognostic 
and therapeutic targets.However,the knowledge about circRNAs remains poor.In 
addition to the not completely resolved functions and generation mechanisms of 
circRNAs,the annotations of circRNAs are also waiting for expanding.Here,we 
review the generation mechanisms,biological functions,and application of 
circRNAs in tumor research,aiming to provide integrated information for the 
future research.