Squamous cell carcinoma of the renal pelvis with metastasis in a dog.

The gross and microscopical features of a squamous cell carcinoma of the renal pelvis in an 18-year-old dog are described. This is a rare tumour originating from transitional cells of the pelvis. The tumour, which invaded the renal parenchyma and capsule and the small intestinal wall, metastasized to the lungs. Tumour cells expressed cytokeratin 8 and were arranged in a pattern similar to that of a squamous cell carcinoma found elsewhere, with prickle cells and horny pearls. The tumour was not diagnosed clinically but was found at necropsy. The presence of pelvic calculi in this dog is suggested as a cause of transitional cell squamous metaplasia and malignant transformation.