TET1 contributes to the progression of 5‐FU resistance through DNA demethylation of nuclear factor‐erythroid 2‐related factor 2 (Nrf2) and heme oxygenase‐1 (HO‐1) in colon cancer.21 Additionally, a new study suggested that TET1 promotes cisplatin resistance via demethylating the vimentin promoter in ovarian cancer.15 However, little is known about the potential role of TET1 in gemcitabine resistance of CCA. This evidence concerns the gene TET1 and cholangiocarcinoma.