CHAPTER 51 Urinary Tract Tumors
RENAL TUMORS
INCIDENCE
Primary renal tumors are rare in cats. Lymphoma is the neoplasm that affects the kidneys of cats most commonly; other reported tumors include renal adenoma, renal adenocarcinoma, and transitional cell carcinoma.1–3 Less common considerations are nephroblastoma or hemangiosarcoma.1 Involvement of both kidneys does not exclude neoplasia, because bilateral disease has been reported with both lymphoma and renal adenocarcinoma.4,5 Other differential diagnoses for enlarged kidneys, especially for cats with bilateral disease, include polycystic kidney disease or perirenal pseudocysts. It is possible, albeit rare, for cats to have concurrent polycystic kidney disease or perirenal cysts and cancer involving the kidneys.6,7
HISTORY AND PHYSICAL EXAMINATION FINDINGS
Lymphoma involving the kidneys in cats typically is high grade and therefore is a rapidly progressive disease.2,3 Owners may report inappetence or anorexia, lethargy, vomiting, and weight loss in affected cats. Other renal cancers are more slowly progressive and have a more insidious history of gradual weight loss, inappetence, and progressive lethargy. Signs of paraneoplastic syndromes occasionally manifest first; for example, seizures secondary to tumor-associated polycythemia.8
On physical examination the kidneys may be enlarged unilaterally or bilaterally. Renal tumors are nonpainful, smooth to lobulated, soft to firm masses. Although rare, polycythemia secondary to renal tumors may be associated with dark red gingival membranes and/or a heart murmur.1,8
DIAGNOSTIC EVALUATION
The diagnostic evaluation of suspected renal tumors is divided into an assessment of the kidney mass and investigation of whether the tumor has spread elsewhere in the body. Although abdominal radiography and compression radiography may help to localize a lesion to the kidney, ultrasonography is the noninvasive diagnostic tool used most commonly for cats with renal masses.9,10 The finding of hypoechoic subcapsular thickening on ultrasound examination is strongly supportive, but not definitive for, a diagnosis of lymphoma.10 Diagnosis of lymphoma or carcinoma may be obtained through cytological evaluation of a fine-needle aspirate sample11; either ultrasound-guided core biopsy or surgical biopsy of the mass may be required for definitive diagnosis in some cases.
Evaluation for systemic involvement includes a CBC, serum chemistry profile, urinalysis, thoracic radiographs (e.g., pulmonary metastasis check), and a complete abdominal ultrasound. All cats with renal lymphoma should be tested for feline leukemia virus (FeLV), because up to 50 per cent are reported to be positive.12 Typically renal tumors are associated with anemia; however, polycythemia has been reported in cats with renal tumors.1,8 The most likely causes of this interesting paraneoplastic syndrome are excessive erythropoietin production by tumor cells or renal hypoxia. The serum chemistry profile, in conjunction with urine specific gravity, is used primarily to assess the degree of azotemia because this may affect how well cats tolerate surgical or chemotherapeutic intervention. Although a urine sediment examination is recommended, tumor cells rarely exfoliate into the urine. Assessment of contralateral renal function by scintigraphy or pyelography often is recommended prior to nephrectomy.
Greater than 50 per cent of cats with renal or transitional cell carcinoma have metastatic disease to the regional lymph nodes or lungs, and it is unusual for cats with renal lymphoma to have disease localized solely to the kidneys.1,12 Furthermore, renal lymphoma is associated with central nervous system (CNS) involvement, and it is reported that 40 per cent of the deaths in cats with renal lymphoma are as a result of CNS involvement.12
TREATMENT AND PROGNOSIS
Renal Adenoma
Because these are benign tumors, treatment with complete surgical excision should be curative.
Renal Carcinoma/Adenocarcinoma/Transitional Cell Carcinoma
The treatment of choice for renal adenocarcinoma is surgical excision. Although the percentage of cats who go on to develop metastatic disease is not known, pulmonary metastasis following surgical excision has been reported.8 Further, the disease also has been reported to affect both kidneys simultaneously.5 Therefore chemotherapy is indicated but the drug, or drug combination, with best efficacy is not known. Human beings with renal carcinoma are treated with a combination of surgery, cisplatin chemotherapy, immunotherapy with either interleukin-2 or interferon alpha, and tyrosine kinase receptor inhibitors.13 Because cisplatin is fatal to cats, carboplatin therapy (240 mg/m2 IV q21d)14 could be considered.
Nephroblastoma
Although reported very rarely in cats and dogs, this tumor arises from embryonal tissues and typically is well encapsulated although metastases may occur.15 Malignant nephroblastoma, reported in one cat, is treated surgically. The effect of chemotherapy is unknown, and prognosis depends on extent of disease and ability to remove the tumor surgically.
Hemangiosarcoma
Although less common than in dogs, visceral hemangiosarcoma in cats often is associated with hemorrhage, metastasis, and a short survival time.16–18 The ability to excise the tumor completely is associated with a better outcome.18 Chemotherapy with carboplatin has been associated with complete remission of short duration (<168 days) in one cat with subcutaneous hemangiosarcoma.14 For dogs with visceral hemangiosarcoma, treatment with a doxorubicin-based chemotherapy protocol prolongs survival.19–21
Lymphoma
Because of the systemic nature of the disease, cats with renal lymphoma are treated with chemotherapy. A combination chemotherapy protocol utilizing vincristine, cyclophosphamide, doxorubicin, and prednisone ± L-asparaginase (CHOP) is recommended.22 Although median survival times of 266 days have been reported in cats with various forms of lymphoma treated with cyclophosphamide, prednisone, and vincristine,23 other reports support the addition of doxorubicin to lymphoma chemotherapy protocols.24 Furthermore, because of the common association of renal lymphoma with CNS involvement, many oncologists recommend that cyclophosphamide be substituted out for cytosine arabinoside, because this drug reaches cytotoxic concentrations within the CNS.
Along with the chemotherapy protocol utilized, prognostic factors for cats with lymphoma include clinical substage (e.g., whether the animal is ill or well at the time of diagnosis), FeLV status, and response to therapy.24 Although there are no recent case series of cats with renal lymphoma treated with a doxorubicin-based combination chemotherapy protocol, it is the opinion of these authors that FeLV-negative cats with a good response to chemotherapy can have a median survival of 12 months or longer.
LOWER URINARY TRACT NEOPLASIA
BLADDER TUMORS
Incidence and Risk Factors
Neoplasia of the feline lower urinary tract represents a very small portion of lower urinary tract disease. Incidence rates for primary bladder tumors vary from 0.07 per cent to 0.38 per cent of all tumors in cats.25–27 This is far lower than that reported for human beings and dogs. One possible reason for the lower incidence observed in cats is the difference in tryptophan metabolism among the species. Unlike dogs and human beings, cats produce very small quantities of the renally excreted tryptophan metabolites, ortho-aminophenol in particular, which can accumulate in the bladder and act as a carcinogen.25,28
In other species environmental toxins and exposure to chemicals such as herbicides and insecticides play a large role in the development of transitional cell carcinoma (TCC).27,29 TCC is the most common form of bladder cancer found in the human being, dog, and cat.25–2729 There is no known association between exposure to these carcinogens and bladder tumor development in cats. However, there are very few cases reported in the literature, so evidence for or against these risk factors is lacking. Associations between bladder cancer and neuter status, body condition score, and exposure to cyclophosphamide can not be made in cats for the same reasons.
Nevertheless, a few risk factors can be determined using the information that has been published to date. Like human beings, male cats are at an increased risk of developing TCC.27,29,30 Older cats are affected routinely. The average age of affected cats typically is over 9 years of age.27,29–31
Cyclooxygenase-2 (Cox-2) overexpression has been identified in cats with TCC of the bladder. Reports of four fishing cats (Prionailurus viverrinus) diagnosed with TCC indicated Cox-2 overexpression in most samples tested.32,33 Another study looking at various tumors of domestic cats revealed that seven of 19 cats with TCC of the bladder had Cox-2 overexpression.34 Whether Cox-2 overexpression is related to malignant transformation or progression of the tumor remains to be seen.
Other reported primary bladder tumors in the cat include non–TCC (squamous cell carcinoma, undifferentiated carcinoma, and adenocarcinoma), leiomyoma, leiomyosarcoma, hemangiosarcoma, lymphoma, and fibroma.27,31 These tumors all are extremely rare. No information regarding incidence or risk factors for these tumors is available in the literature.
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