In mouse cancer cells, circ-Foxo3 suppresses cell cycle progression by interacting with cyclin-dependent kinase 2 (CDK2) and cyclin-dependent kinase inhibitor 1 (p21) to form a circFoxo3-p21-CDK2 ternary complex, thereby arresting the functions of p21 and CDK2 in cell cycle regulation (52). The gene discussed is CDK2; the disease is cancer.