Additional Study Information: This study is designed to evaluate the efficacy and safety of the study drug AG-120 as compared to placebo in patients with advanced cholangiocarcinoma. AG-120 blocks an abnormal form of a protein called IDH1, which is involved in cancer cell metabolism. Abnormal IDH1 causes too much of a substance called 2-HG to be produced. Researchers believe that having too much 2-HG may fuel cancer growth. Patients in this study must have cholangiocarcinoma that contains a mutated form of the IDH1 gene. Patients will be randomly assigned to receive either AG-120 (orally) or placebo. The placebo is a pill that looks exactly like AG-120, but does not contain any AG-120.