Abstract
Ectopic pancreatic tissue can occasionally cause inflammation, hemorrhage, stenosis, and invagination, similar to normal pancreatic tissue; however, tumorigenesis is rare. This case report describes an ectopically observed pancreatic acinar cell carcinoma in the thoracic cavity of a female Fischer (F344/DuCrlCrlj) rat. Histopathologically, polygonal tumor cells with periodic acid-Schiff-positive cytoplasmic eosinophilic granules showed solid proliferation and infrequently formed acinus-like structures. Immunohistochemically, the tumor cells were positive for cytokeratin, trypsin, and human B-cell leukemia/lymphoma 10, which specifically reacted with pancreatic acinar cells, and negative for vimentin and human α-smooth muscle actin. Ectopic pancreas develops in the submucosa of the gastrointestinal tract; however, there are few reports of its development and neoplasia in the thoracic cavity. To the best of our knowledge, this is the first report of ectopic pancreatic acinar cell carcinoma in the thoracic cavity of a rat.