| Neoplasms of the kidney are uncommon and represent ~0.5-1.7% of all neoplasms in dogs. Benign neoplasms are uncommon, usually incidental findings at necropsy, and generally of little clinical significance. Adenomas, lipomas, fibromas, and papillomas have been reported. |
| Primary malignant renal neoplasms (except nephroblastomas) are most common in middle-aged to older animals. No breed predilection has been found, except for heritable predilection for the development of bilateral, multifocal cystoadenocarcinomas in German Shepherds, generally between 5-11 yr of age. The most common primary malignant renal neoplasm is carcinoma, which originates from the renal tubular epithelium. Usually, it is unilateral, located at one pole of the kidney, and well
demarcated. Size varies from microscopic to several times that of the normal kidney, and color may be yellow, white, or gray. Renal carcinomas metastasize early to various organs; the opposite kidney, lungs, liver, and adrenals are involved most commonly. |
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Nephroblastomas
(embryonal nephroma, Wilms’ tumor) arise from vestigial embryonic tissue. They are seen in young animals and, in dogs, are most commonly diagnosed at <1 yr of age. There is no breed predilection. Males are affected twice as commonly as females. Nephroblastomas are usually unilateral but are occasionally bilateral. They can grow to immense proportions; it is not uncommon to have
virtually the entire abdomen occupied by tumor. Metastasis occurs to regional lymph nodes, liver, and lungs. |
| Transitional cell carcinomas arise from transitional epithelium of the renal pelvis, ureter, bladder, or urethra (see
neoplasms of the lower urinary tract,
Neoplasms of the Lower Urinary Tract). Other primary malignant renal neoplasms are uncommon and include hemangiosarcomas, fibrosarcomas, leiomyosarcomas, and squamous cell carcinomas. |
| The kidneys are a common site of metastatic or multicentric neoplasms. Metastatic lesions may be unilateral or bilateral. Lymphosarcoma is the most common multicentric tumor involving the kidneys. Up to 50% of dogs and cats with lymphosarcoma have renal lesions and, in some cases, only the kidneys or kidneys and brain are affected. Renal involvement is usually multifocal or diffuse, interstitial, and bilateral, and results in large, irregular kidneys. Lymphosarcoma in cats
frequently is associated with infection by feline leukemia virus. |
| Clinical Findings: |
| Signs are nonspecific and may include weight loss, anorexia, depression, and fever. Bilateral neoplasms may uncommonly destroy sufficient renal tissue to cause chronic kidney disease and associated signs of uremia. Astute owners may notice “lumps” in their animal’s abdomen or abdominal enlargement. Persistent hematuria, usually microscopic, may occur. Rarely, renal tumors may produce excessive erythropoietin, which results in erythrocythemia (
Polycythemia: Introduction). |
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| Diagnosis: |
| History and clinical signs may indicate a mass in the area of the kidneys or renomegaly, which can be confirmed by ultrasonography or radiography, although an excretory urogram or renal arteriogram may be required. Radiographs of the thorax may reveal metastatic disease. Neoplastic cells occasionally can be found in the urine sediment. Percutaneous needle aspiration and cytologic examination may be sufficient for the diagnosis of lymphosarcoma in cats and dogs, particularly
when there is diffuse involvement or with ultrasonographic guidance when multifocal disease occurs. Histologic examination of tissue obtained by needle biopsy or surgical wedge biopsy is often necessary to determine the type of tumor. |
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| Treatment: |
| Treatment of all renal neoplasms except lymphosarcoma involves surgical removal; unilateral nephrectomy is usually required. Lymphosarcoma is best managed by combination chemotherapy (see
canine malignant lymphoma,
Canine Malignant Lymphoma: Introduction). Chemotherapy is generally ineffective against renal tumors other than lymphosarcoma. |
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