Pro-metastatic circRNAs, such as circKIF4A and circBACH1, promote metastasis by modulating signaling pathways such as the STAT3 and PI3K/AKT pathways, whereas tumor-suppressive circRNAs, including circFOXO3 and circNFIB, inhibit metastatic progression through mechanisms such as VEGF downregulation and the suppression of arachidonic acid metabolism. The gene discussed is STAT3; the disease is neoplasm.