Complex Urothelial Carcinoma with Micropapillary and Nested Variant with Tubular Differentiation and Omental Metastasis in a Dog: A Case Report

In this presentation, the pathological examination of a complex micropapillary and nested urothelial carcinoma, tubular variant, diagnosed in the renal pelvis of a 1.5-year-old male Wolfdog, along with omental metastasis, is presented. The owner brought their dog to Selçuk University Veterinary Faculty Animal Hospital with complaints of bloody urine and a mass in the abdominal region upon palpation. During the clinical examination, a large mass was detected in the left kidney during the ultrasonographic examination. During the surgical removal of the kidney, masses were also observed in the omentum and samples were taken. The tissues were sent to the Pathology Laboratory of Selçuk University Faculty of Veterinary Medicine for histopathological examination. Macroscopic examination revealed that the mass in the kidney was 20x13x11 cm in size, creamy pink in colour, soft in consistency, and multilobular in structure. Microscopic examination revealed that significant atypia, pleomorphism, mitotic figures, cells with nuclei pushed to the periphery, signet ring cells, and Melamed-Wolinska bodies in the tumour cells. The diagnosis was nested variant urothelial carcinoma and omentum metastasis, showing micropapillary and tubular differentiation due to the presence of tubular and micropapillary structures formed by tumour cells.