For example, orotate phosphoribosyl transferase (OPRT) is associated with activation of 5-FU into FdUMP, and a reduced expression of OPRT has been found to be associated with poor response to 5-FU in CCA, suggesting that OPRT could be used as a predictor for the response to 5-FU in CCA (118). This evidence concerns the gene UMPS and cholangiocarcinoma.