LGR5 and biliary tract neoplasm: The potential sources of these damage-induced Lgr5+ stem cells include Lgr5− progenitor cells from the noninjured liver23, recruitment from distant sites (e.g., mesenchymal cells)24, Axin2+ hepatocytes surrounding the central vein25, Sox9+ hybrid periportal hepatocytes around the portal vein and biliary tree26, or transdifferentiation of hepatocytes into ductal cells, as that occurs in tumors of the biliary tree (intrahepatic cholangiocarcinoma)27.