Circular RNAs (circRNAs) are a class of newly-identified non-coding RNA 
molecules. CircRNAs are conserved across different species and display specific 
organization, sequence, and expression in disease. Moreover, circRNAs' closed 
ring structure, insensitivity to RNase, and stability are advantages over linear 
RNAs in terms of development and application as a new kind of clinical marker. 
In addition, according to recent studies, circular RNA-7 (ciRS-7) acts as a 
sponge of miR-7 and thus inhibits its activity. Numerous evidences have 
confirmed expression of miR-7 is dysregulated in cancer tissues, however, 
whether ciRS-7 invovled in oncogenesis by acting as sponge of miR-7 remains 
unclear. Most recently, a study reported ciRS-7 acted as an oncogene in 
hepatocellular carcinoma through targeting miR-7 expression. This suggest 
ciRS-7/ miR-7 axis affects oncogenesis, and it provides a new perspective on the 
mechanisms of decreased miR-7 expression in cancer tissues. Discovery of sponge 
role of circRNAs caused researchers to more closely explore the underlying 
mechanism of carcinogenesis and has significant clinical implications, and may 
open a new chapter in research on the pathology and treatment of cancers. This 
review summarizes the structure and function of circRNAs and provides evidence 
for the impact of ciRS-7 in promoting the development of cancer by acting as 
sponge of miR-7.