Primary renal neoplasia, or cancer that originates in the kidney, is rare in the dog and cat, accounting for less than 2.5 percent of all tumors. The most common tumors in dogs in descending order are renal carcinoma, transitional cell carcinoma, renal adenoma, sarcoma, nephroblastoma, lymphoma and fibroma. The majority of tumors seen are malignant, and metastatic tumors that spread from another place are more common than primary tumors. There are a host of possible presentations associated with renal tumors.

Individuals may have no clinical signs early in the disease process. The classic triad of physical findings in cats and dogs with renal tumors includes abdominal mass, weight loss, and in a subset of cases, blood in the urine (hematuria), although abdominal and/or back pain is not uncommon. Anemia (low red blood cell count) and renal failure (azotemia) are not uncommonly found in these patients, especially when both kidneys are involved. Depending on the specific case, specific diagnostics and therapeutics would be recommended and tailored to the individual.

Several diseases and disorders have similar symptoms to renal neoplasia. These include:

Pyelonephritis, or an infection of the kidney

Hydronephrosis, which is the enlargement of the pelvis of the kidney with urine, as a result of obstruction of the ureter – the tiny tubular structure that allows the passage of urine from the kidney to the urinary bladder

Renal hematomas or blood clots secondary to trauma

Ethylene glycol toxicosis after ingestion of antifreeze that causes bilateral kidney enlargement (renomegaly) due to the formation of calcium oxalate crystals, which are particles that form in the kidneys from antifreeze

Leptospirosis, an infectious disorder that causes bilateral renomegaly and renal failure in dogs

Urolithiasis (stones) anywhere throughout the urinary tract, especially in the kidney

Chronic renal failure associated with or as a result of renal neoplasia

Renal abscesses, or localized pockets of pus within the kidney, that usually cause unilateral renomegaly in cats and dogs.

Perirenal pseudocysts, the accumulation of fluid between the kidney and its surrounding capsule.

Glomerulonephritis, which is an inflammation of the glomeruli of the kidney

Amyloidosis, which is the deposition or collection of a type of protein in organs and tissues that compromises normal function

Other abdominal masses in the pancreas, ovaries, liver or adrenal glands that can cause abdominal distension and similar signs

Other causes of abdominal discomfort, including pancreatitis and peritonitis, which is inflammation of the abdominal cavity

Disorders associated with back pain such as intervertebral disc protrusion or a spinal infection or tumor

Disorders that cause excessive thirst and urination to include hyperadrenocorticism (Cushing's disease), diabetes mellitus and liver disease

Coagulopathies, or clotting disorders, such as thrombocytopenia (decreased platelet count) or warfarin toxicity (rat poison), that cause bloody urination

Polycythemia is a disorder that causes the red blood cell count to rise. It can be a primary or secondary disorder, and is occasionally seen associated with some renal tumors.