Although the K19CreERT mouse strain achieves similar recombination efficiencies across the different portions of the biliary tree, activation of the Kras oncogene and concomitant deletion of the Tgfβr2 and Cdh1 (E-cadherin) in adult K19 positive cells led to CCA development predominantly in the extrahepatic and perihilar bile ducts. The gene discussed is KRAS; the disease is cholangiocarcinoma.