Origin and Development of the Precursor Lesions in Experimental Pancreatic Cancer in Rats

Notwithstanding the importance of understanding how pancreatic ductal adenocarcinoma develops, the process remains controversial. A key question is whether the cells of origin of the tubular complexes that constitute precursor lesions are derived from a single cell type or from multiple types. Suggestions that they arise solely from centroacinar cells or ductal cells have been based on inference due to their morphologic appearance in tissue from patients or investigation of limited numbers of tubular complexes in animal models later in the carcinogenic process. The present study establishes clearly that two steps are involved; rapid transdifferentiation to produce tubular complexes followed later by transformation of the component cells. Animals were killed at intervals beginning 1 day after implantation of the carcinogen dimethylbenzanthracene. Transdifferentiation of acinar cells to ductal cells does not require cell division. Transition of lobules to tubular complexes begins by 2 days after implantation of carcinogen. Within 4 days after implantation well-developed tubular complexes are present. Islets participate in the process. Ductal adenocarcinoma is observed by 1 month after implantation of carcinogen. Chymotrypsin and cytokeratin localized by immunocytochemistry indicate acinar and ductal cell characteristics. Acino-ductal transdifferentiation persists in carcinogen-implanted animals, but not in controls implanted with sodium chloride crystals or subjected to sham implantation. The precursor lesions (tubular complexes) are formed by the transdifferentiation of acinar cells and to a lesser extent islet cells, with the incorporation of the duct cells pre-existing in the lobules. Therefore, cells that at one time were acinar cells, islet cells, and duct cells, provide the precursor cells for the ductal adenocarcinoma that develops from tubular complexes. The results raise the question whether the transdifferentiated cells in the tubular complexes of patients with chronic pancreatitis are more susceptible to carcinogenic influences, resulting in the increased rate of pancreatic cancer.