TET1 and cholangiocarcinoma: A considerable number of studies have been conducted to investigate the expression of TET1 in various cancers.[18] The results of these studies have demonstrated that there are discrepancies in the expression of TET1 in different types of tumors, with varying effects on patient prognosis.[19] To investigate the expression of TET1 in CCA, an immunohistochemical (IHC) analysis was performed on an extrahepatic CCA (ECCA) tissue microarray (TMA) consisting of 36 CCA tissues pathologically confirmed and 9 normal tissues.