KRT19 and neoplasm: The designation of low tumor burden was assigned when the animal had pancreatic intraepithelial neoplasms (PanINs) and the structures of pancreatic ducts and acini were maintained, as depicted in the left panel of Fig. 3A. High tumor burden was assigned when the tumor weight exceeded 10% of the body weight and tissues exhibited invasive disease, a loss of tissue architecture and a loss of epithelia with abundant stroma, as depicted in the right panel of Fig. 3A. Invasive disease was scored when ductal cells, which stain positive for CK19, were detected in the stromal compartment.