Renal cell carcinoma is a cancer arising from the epithelial cells of the kidney tubules — the microscopic structures responsible for filtering blood and producing urine. It is the most common primary malignant kidney tumour in dogs, though it remains uncommon overall. The tumour is usually unilateral (affecting one kidney), and surgical removal of the affected kidney (nephrectomy) can be curative if the cancer has not spread. Many cases are found incidentally during abdominal imaging for other reasons. German Shepherd Dogs have a hereditary predisposition through a specific gene mutation (in the BHD/folliculin gene) that causes a distinct form called renal cystadenocarcinoma. Prognosis depends on whether the cancer has spread at the time of surgery and on the tumour's microscopic features, particularly how actively the cells are dividing.