KLK4 and cancer: This highly expressed circRNA was reported to enhance cell proliferation, invasion and migration by targeting miR-637 to regulate the expression of Kallikrein-related peptidases 4 (KLK4), and KLK4 was reported to be involved in many steps of OvCa tumorigenesis and progression and to exert modulatory effects on a subset of cancer-related genes and proteins in several cancers [62, 63].