F-circEA [41], circ-CCAC1 [42], circ-N4BP2L2 [43] and circ-RNF220 [44] were abundantly expressed in human peripheral blood, which could be used as the biomarkers for diagnosis of EML4-ALK-positive non-small cell lung cancer, cholangiocarcinoma, epithelial ovarian cancer and pediatric acute myeloid leukemia, respectively. Here, N4BP2L2 is linked to cholangiocarcinoma.