The study drug, varlitinib, is an investigational anti-tumor product, delivered in the form of tablets. The study drug has been administered as a single and combination treatment to patients with metastatic gastric cancer, gastro-esophageal tumors, breast cancer, and biliary tract cancer (BTC). Laboratory studies and animal research suggest that the study drug stops cancer cells from growing by affecting different kinds of proteins in cancer cells. In particular, laboratory studies suggest that the study drug may be effective in targeting and inhibiting (preventing) the pathways of certain proteins in cells called “HER” (human epidermal growth factor receptor). The “HER” protein is important in types of cancer such as cholangiocarcinoma (BTC), gastric cancer, breast cancer, and others. Varlitinib has shown activity in BTC. In this study, patients will receive study drug plus capecitabine, or placebo plus capecitabine. Inclusion allows all forms of BTC and there is no biomarker-based patient selection.