Cholangiocarcinoma is frequently associated with a marked desmoplastic response of abundant fibrous stroma, which can be focally calcified, and there is frequently an accompanying acute on chronic inflammatory reaction (Fig. 6). Mucin and bile might be incorporated in the stroma and the tumour can abut directly onto hepatocytes and infiltrate along adjacent portal tracts so that they mimic non-neoplastic bile ducts. Fibrous encapsulation does not occur. Lymphovascular and perineural invasion can be seen, especially in large portal tracts. Varying degrees of atypia can be found in the epithelium lining dilated ducts adjacent to the tumour, especially in the intraductal type (Fig. 7), and the transition from benign to dysplastic to frankly neoplastic epithelium can sometimes be difficult to demarcate.