Urachal Carcinoma in a Young Adult Dog

Introduction: Tumours arising from embryonal remnants are rare; among these urachal carcinoma (UC) is reported sporadically in man, mostly in adult and aged patients, and less frequently in children and adolescents. To our knowledge UC has never been reported in dogs. Materials and Methods: An 18-month-old, male, Labrador retriever dog was referred for abdominal pain. Ultrasonography revealed multiple large (up to 25 cm) cystic abdominal masses, adherent to the omentum and close to the pancreas and spleen. The largest mass was removed surgically and formalin fixed for histology. Immunohistochemistry with antibodies against cytokeratin and uroplakin III was also performed. Computed tomography examination did not reveal findings compatible with metastatic lesions. A postoperative change in chemotherapy was performed. Results: Histologically, a large, multinodular, partially encapsulated, infiltrating, cystic neoplasm, involving mesenteric fat was observed. The neoplasm was composed of small cystic structures lined either by simple columnar epithelium with intermingled goblet cells (intestinal type) or by pseudostratified epithelium with 4e5 rows of nuclei and occasionally superficial luminal ‘umbrella’ cells (urothelial type). Immunohistochemically, all neoplastic cells were intensely and diffusely cytokeratin positive. In urothelial type areas, neoplastic cells also showed intense intracytoplasmic expression of uroplakin III. Twelve months after surgery, the dog is still alive and in very good clinical condition without relapse. Conclusions: UC is rare in human medicine and is characterized by double intestinal (colonic) and urothelial differentiation. Metastatic cases are reported, with variable fates. The present case is the first report of UC in dogs. The diagnosis was possible based on both histology and immunohistochemistry.