+ General Considerations

  • Renal LSA is the most common renal tumor in cats, followed by renal carcinoma and nephroblastoma
  • Mesenchymal tumors are rare (5% in cats) but are aggressive and highly metastatic
  • Mesenchymal renal tumors include HSA, FSA, CSA, and leiomyosarcoma
  • Benign tumors have been reported but, except for hemangioma, are usually asymptomatic and incidental findings
  • Benign tumors include hamartoma (= hemangioma, fibroma and intrarenal lesions such as myxoma, lipoma and mixed tumors), leiomyoma, fibroma, adenoma, papilloma, lipoma, and perithelioma
  • Adenoma is reported to cause nephrosclerosis in man and hypertrophic osteopathy in a cat
  • Metastatic tumors are common in the kidney because of the large blood supply and abundant capillaries

Renal Lymphosarcoma

+ General Considerations

  • LSA is the most common renal tumor in cats
  • Renal involvement is observed in up to 45% of cats with multicentric LSA
  • Middle-aged, male cats are usually affected and retroviruses, such as FeLV and FIV, are frequently associated with feline LSA

+ Clinical Features

  • Diagnosis: percutaneous FNA or renal biopsy
  • Staging is performed with palpation, hematology, serum biochemistry, survey abdominal radiographs or ultrasonography, and bone marrow aspiration



  • Clinical signs are non-specific such as abdominal enlargement and abdominal pain
  • Urinary signs are uncommon
  • Skin lesions (i.e., dermatofibrosis) are associated with renal cystadenocarcinomas in GSD
  • Lameness caused by either skeletal metastases or hypertrophic osteopathy
  • Paraneoplastic polycythemia may be more common with renal tumors as majority of renal carcinomas involve the proximal convoluted tubule which is the main site of erythropoietin production

+ Urinalysis and Urine Sediment Cytology

  • Proteinuria is a common finding with renal tumors
  • Hematuria is uncommon with renal carcinoma, but can be seen with HSA, hemangioma, and renal pelvis TCC
  • Urine sediment cytology is rarely diagnostic for renal tumors

+ Blood Tests

  • Hematology and serum biochemistry findings are usually normal or non-specific
  • Mild-to-moderate normochromic, normocytic anemia can be caused by either hematuria or bone marrow suppression secondary to chronic disease
  • Polycythemia is a reported paraneoplastic syndrome with renal tumors
  • Uremia may result from obstruction of urinary outflow, bilateral renal tumors, or age-related renal failure


+ General Considerations

  • Survey abdominal and thoracic radiographs, contrast radiography, ultrasonography, CT, and MRI are imaging modalities used to identify the presence and extent of renal tumors

+ Survey Abdominal Radiography

  • Survey abdominal radiographic findings: sublumbar lymph node enlargement, renomegaly, and skeletal metastases, especially lumbar vertebrae and pelvis
  • Abdominal mass is identified in 81% and localized to the kidney in 54% of dogs with primary renal tumors
  • Focal mineralization can be observed but difficult to differentiate tumor from renal calculi and GI opacities

+ Excretory Urography

  • Excretory urographic findings: space occupying renal mass, variable opacification of the renal parenchyma, and distortion of the renal pelvis
  • Excretory urography successfully identifies a renal mass in 96% dogs with primary renal tumors

+ Ultrasonography

  • Ultrasonography results in earlier diagnosis and more successful treatment of renal neoplasia in humans
  • Renal tumors, except for LSA, produce a mixed echogenicity with disruption of the normal renal architecture
  • Renal LSA is usually hypoechoic
  • Ultrasonography is also useful in detecting neoplastic involvement of regional lymph nodes and adjacent structures such as the adrenal glands ± caudal vena cava

+ Advanced Imaging

  • CT scans are used for the diagnosis and local staging of renal neoplasia with a high correlation between CT findings and gross pathology
  • MRI is preferred for identifying adjacent vascular and visceral invasion, especially if renal-sparing surgery is planned
  • Other imaging techniques include caval venography and nuclear scintigraphy

+ Biopsy

  • Biopsy is required for definitive diagnosis of renal tumors
  • Biopsy techniques: FNA, needle biopsy, and wedge biopsy
  • FNA and needle-core biopsy can be performed using a blind, ultrasound-guided, laparoscopic, or open technique
  • Ultrasound-guided biopsy is a rapid, safe, and accurate technique for diagnosing focal and diffuse renal disease
  • Blind percutaneous needle biopsy can be performed in cats where the kidney can be immobilized by palpation
  • Percutaneous biopsy should be performed with bilateral renal lesions or suspected renal LSA
  • Single procedure surgical biopsy, staging, and definitive treatment preferred for unilateral lesions
  • Complications of needle biopsy: minor localized hemorrhage, microscopic hematuria, and tumor seeding

Clinical Staging


+ General Considerations

  • Surgical management depends on behaviour of the tumor, presence of metastases and bilateral renal involvement, and invasion of the caudal vena cava and adjacent structures
  • Nephroureterectomy is recommended for:
  • Malignant renal and ureteral tumors except LSA
  • Grading and staging of nephroblastoma
  • Nephron sparing techniques should be used for benign tumors and bilateral disease to reduce the risk of renal failure


+ Chemotherapy and Immunotherapy for Renal Cell Carcinoma

  • Renal carcinoma is considered resistant chemotherapy, hormonal therapy, and radiation therapy
  • Response rates to chemotherapy are < 10% and chemoresistance is most likely caused by the presence of the multidrug resistance p170 glycoprotein on the surface of tumor cells
  • Multiple chemotherapeutic agents do not improve response rates but increases toxicity
  • Current investigations in humans include combining vinblastine with immunotherapy or multidrug resistant antagonists such as cyclosporine analogues, tamoxifen, or verapamil
  • Immunotherapy using agents such as recombinant IL-2 and IFN-λ have provided encouraging results
  • Immunotherapy was investigated as nephroureterectomy resulted in regression of metastatic lesions in humans with renal carcinoma due to an enhanced immune response, however, this effect has not been observed in animals
  • Immunotherapy and chemotherapy have not been investigated in cats or dogs with renal carcinoma

+ Chemotherapy and Radiation Therapy for Nephroblastoma

  • Surgical resection and chemotherapy is recommended for all stages of nephroblastoma in children
  • Vincristine and actinomycin D are recommended for all stages
  • Doxorubicin is added for stage II tumors with unfavorable histology and stage III tumors with favorable histology
  • Actinomycin D has been used in canine nephroblastoma with partial responses and prolonged survival times
  • Neoadjuvant chemotherapy is recommended for large inoperable tumors, bilateral disease, and neoplastic involvement of the caudal vena cava
  • Radiation therapy is recommended for stages III and IV tumors with favorable histology and stage II-IV tumors with unfavorable histology
  • Principal concerns in children are the effects of chemotherapy and radiation therapy on developing organs as children are more sensitive to the cardiotoxic effects of doxorubicin and radiation therapy can affect development of the lungs and spine


+ Feline Renal Lymphosarcoma

  • Stage, degree of response, FeLV status, and renal function are prognostic factors for cats with renal LSA
  • Mean DFI 372 days
  • Mean survival time 408 days with a 61% CR
  • Mean survival time is significantly better for cats with a CR compared to PR (408 days v 75 days)
  • Mean survival time is significantly better for FeLV-negative cats (610 days v 267 days)
  • Mean survival time is significantly better for cats with mildly abnormal renal function than those with moderate to severe abnormalities



Stage Description
I Single tumor (extranodal) or single anatomic area (nodal)
II Single tumor (extranodal) with regional lymph node involvement 2 extranodal tumors ± regional lymph node involvement on the same side of the diaphragm Primary resectable GI tumor (i.e., ileocecal) ± mesenteric lymph node involvement ≥ 2 nodal areas on the same side of the diaphragm
III 2 extranodal tumors either side of the diaphragm ≥ 2 nodal areas on either side of the diaphragm Diffuse unresectable intra-abdominal tumors Paraspinal and epidural tumors regardless of other tumor sites
IV Stage I-III with liver ± spleen involvement
V Stage I-IV with CNS ± bone marrow involvement
T0 No evidence of neoplasia
T1 Small tumor without deformation of the kidney - Primary Tumor
T2 Single tumor with deformation ± enlargement of the kidney
T3 Tumor invading perinephric structures ± pelvis or ureter ± renal blood vessels
T4 Tumor invading adjacent organs
M0 No evidence of metastasis
M1 Evidence of distant metastasis with site specified with (a) single metastasis, (b) multiple metastasis in 1 organ, and (c) multiple metastasis in ≥ 2 organs - Metastasis
N0 No evidence of regional lymph node involvement
N1 Ipsilateral regional lymph node involvement - Node
N2 Bilateral regional lymph node involvement
N3 Distant lymph node involvement