APEX1 and cholangiocarcinoma: Since overexpression of APEX1 was observed in several other cancers, serum APEX1 level of CCA patients should be compared with that of other cancer patients, especially hepatocellular carcinoma, pancreas cancer, or other metastatic liver cancers, etc. Besides, the function of APEX1 should be further analyzed in relation to the signal pathway for metastasis mechanisms.