Emerging Roles of Circular RNAs in Osteosarcoma

Osteosarcoma (OS) is a primary malignant bone tumor in early adolescence with high metastasis and death rates. Although the combination of polychemotherapy and surgical excision increased the survival rates up to 60%, the prognosis remains poor for most patients with metastatic or recurrent osteosarcoma. However, the exact pathogenic mechanism and pivotal elements regulating tumor invasion and metastasis are largely unknown. Circular RNAs (circRNAs) are novel endogenous non-coding RNA (ncRNA) molecules that generate the cyclic structure from back splicing. An increasing number of studies show that circRNAs can regulate transcriptional or posttranscriptional gene expression by acting as microRNA (miRNA) sponges and are involved in regulation of many important biological processes. The deregulation of some circRNAs was demonstrated in osteosarcoma. Furthermore, some circRNAs were identified to play essential roles in osteosarcoma occurrence, invasion, and metastasis. This review summarizes the regulatory effect of circRNAs in the occurrence and development of osteosarcoma, concentrating on deregulation, regulatory mechanisms, and functions of circRNAs and their potential value as biomarkers and therapy.