The 1 cm renal mass is well circumscribed and partially encapsulated. The mass elevates the renal capsule and extends almost to the corticomedullary junction. The tumor is subdivided into lobules by a dense fibrovascular stroma. Foci of lymphocytes and plasma cells, hemorrhage and hemosiderin are scattered in adjacent renal interstitial tissue. The tumor is composed of cuboidal to columnar cells forming papillary, cystic, and tubular areas as well as scattered solid areas.
Cells tend to be polygonal in solid areas.
Tumor cells have oval to round nuclei with stippled chromatin. Nuclei are often located at the basilar end of the cell, especially when forming tubules or papillary structures. Mitotic figures are rare. The cells have eosinophilic finely granular cytoplasm with distinct cellular margins. Renal cell carcinoma is the most common renal tumor of dogs, cattle, and sheep.