Circular RNAs: Fundamental mechanisms in tumor metastasis and detection strategies (Review).

 As a class of endogenous non‑coding RNAs, circular RNAs (circRNAs) are produced by an event known as back‑splicing. Although circRNAs were initially considered to be the product of abnormal splicing events, increasing evidence has shown their vital role in the development of various diseases, especially malignant tumors. Tumor metastasis is the leading cause of tumor deterioration and cancer‑associated mortality, and involves biological changes to malignant cells. A number of circRNAs can mediate tumor progression, especially tumor metastasis. Furthermore, due to their unique structural features, circRNAs are highly stable in body fluids, and have temporal and tissue specificity, making them potentially ideal non‑invasive biomarkers for sensitive monitoring of tumor changes. The present review focuses on circRNAs associated with tumor metastasis and discusses their functional mechanisms. Furthermore, the current review summarizes advances regarding circRNAs as biomarkers and detection strategies.