DKK1 and retinoblastoma: For instance, circ_0000527/miR-98-5p/XIAP facilitates the malignant progression of retinoblastoma cells (Yu et al., 2021), and circ_0018414/miR-6807-3p/DKK1 impedes the tumor development in lung adenocarcinoma (Yao et al., 2021).