LAUSR

We appreciate Dr Bannasch’s lengthy and careful response to our recent article. We are certainly aware of Dr Bannasch’s long involvement with this change and are gratified that he has taken the time to comment on our paper, as well as appreciating his excellent history on the research into cholangiofibrosis. As Dr Bannasch points out, the proper description for this change has long been a subject of academic discussion and argument. We felt that the changes present in our case most closely resembled those described by many authors as cholangiofibrosis. In our experience, although the finding has characteristics ascribed to malignant processes, few of these lesions in rats progress to malignancy, invasion, or metastasis. The uniqueness of this lesion, which is apparently restricted to rats, was the basis of our decision to describe the lesion as cholangiofibrosis, rather than a neoplasm. As Dr Bannasch points out, this lesion is extremely rare in untreated animals, which was one of the major reasons for publishing this case. In addition, as working toxicologic pathologists, we try to conform with the recommendations of the International Harmonization of Nomenclature and Diagnostic Criteria (INHAND) whenever possible. In the INHAND guide for the liver, there is no separate term available for a cholangiofibroma. Dr Robert Maronpot (personal communication, 2019) recently stated that “the distinction between cholangiofibrosis and cholangiofibroma is one that does not need to be made. Whether or not the lesion is expansile or compressive or neither is variable, depending on sampling and duration of the lesion. For the INHAND publication, we used cholangiofibrosis and did not have an entry for cholangiofibroma. In retrospect, perhaps we could have indicated that we do not consider cholangiofibroma and cholangiofibrosis to be distinct separate diagnostic entities.” Thus, while we appreciate Dr Bannasch’s scholarship and perspective, we feel that the current lesion is best described as cholangiofibrosis, rather than as a benign tumor. Discussions on the true nature of this change and the best descriptive terminology have been ongoing for close to 50 years. Perhaps with some of the recent advances in molecular pathology, we will be able to arrive at a definitive answer before another 50 years have passed.