Veterinary Society of
Surgical Oncology


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

  • 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
  • atypical or neoplastic lymphocytes can be seen in 15%-60% of cats with LSA
  • 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


  • 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 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 for Renal Lymphosarcoma

  • chemotherapy is recommended for cats with renal or multicentric LSA
  • induction and maintenance protocols using multiple chemotherapeutic drugs have been described
  • chemotherapeutic drugs used include vincristine, cyclophosphamide, L-asparaginase, doxorubicin, methotrexate, and prednisolone


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



No evidence of neoplasia


Small tumor without deformation of the kidney

Primary Tumor


Single tumor with deformation ± enlargement of the kidney


Tumor invading perinephric structures ± pelvis or ureter ± renal blood vessels


No evidence of lymph node involvement


Ipsilateral regional lymph node involvement



No evidence of metastasis


Evidence of distant metastasis with site specified with (a) single metastasis, (b) multiple metastasis in 1 organ, and (c) multiple metastasis in ≥ 2 organs





Single tumor (extranodal) or single anatomic area (nodal)


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


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


Stage I-III with liver ± spleen involvement


Stage I-IV with CNS ± bone marrow involvement


Tumor invading adjacent structures


Bilateral regional lymph node involvement


Distant lymph node involvement

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