GEM and cholangiocarcinoma: Gemcitabine-resistant CCA cell lines (HuCCT1-Gem and SNU-245-Gem) showed an obvious increased tolerance of gemcitabine compared with parental cell lines, with increased half-maximal inhibitory concentration (IC50) of gemcitabine from 10.40 nM to 50.69 nM (HuCCT1 vs. HuCCT1-Gem) and 21.87 nM to 77.62 nM (SNU-245 vs. SNU-245-Gem) (Fig. 1A).