In the absence of evident metastatic disease, the preferred treatment for feline primary renal tumors is removal of the affected kidney. For low-grade renal cell carcinoma or renal sarcoma, this approach may be curative provided renal function remains adequate. Surgical excision is thought to prolong survival in cats with renal cell carcinoma because of the tumor's lower metastatic rate compared with renal transitional cell carcinoma. However, for renal transitional cell carcinoma and most renal cell carcinomas, the long-term prognosis is guarded because of local tumor recurrence or metastasis.³

Adjuvant chemotherapy has been proposed for renal transitional cell carcinoma and renal cell carcinoma, but no standard protocols exist for either of these rare feline tumors. Mitoxantrone chemotherapy caused a partial remission of 60 days in a cat with urinary bladder transitional cell carcinoma.⁶ Carboplatin is safe in cats and has been suggested as an adjuvant treatment for bladder transitional cell carcinoma in cats, although no reports support this use.³ Piroxicam has been used in dogs to successfully treat bladder transitional cell carcinoma, but there are no reports of its use in cats for this purpose.³ These options were considered, and single-agent mitoxantrone chemotherapy was selected for adjuvant treatment of this cat's renal transitional cell carcinoma.

Mitoxantrone is an antitumor antibiotic chemically related to doxorubicin that has been used to treat lymphoma, mammary adenocarcinoma, squamous cell carcinoma, and transitional cell carcinoma in dogs and cats. Its mechanism of action is to inhibit topoisomerase II activity,⁷ and its pharmacokinetics has been described in cats.⁸ One study evaluated the toxicoses and efficacy associated with administering mitoxantrone in cats with various malignant tumors.⁶ Including the partial remission of a cat with bladder transitional cell carcinoma already mentioned, the overall remission rate (complete and partial) for carcinomas was about 18% (nine of 51 cats) in that study. A typical feline treatment regimen is to administer 6 to 6.5 mg/m² intravenously every three weeks. In cats, gastrointestinal side effects were most common. Other reported side effects were myelosuppression, seizures, and secondary sepsis.

Horner's syndrome is a common peripheral neuropathy with many possible causes, including otitis media or interna, trauma, brachial plexus root avulsion, and cranial mediastinal lesions.^10,11 Pharmacologic testing has been described to help localize the lesion in animals with acute Horner's syndrome. When a dilute, direct-acting sympathomimetic agent (e.g. phenylephrine at concentrations of 1% to 10%) is applied topically to the eye, lack of pupillary dilation suggests a preganglionic lesion such as intracranial disease, a C1-T3 myelopathy, or thoracic disease. A positive test result (resolution or improvement of miosis within 20 minutes) should indicate a postganglionic lesion because of the increased sensitivity of local adrenergic nerves after sympathetic denervation.¹² Although as described, pharmacologic testing should be helpful in localizing the site of neuron injury, the specificity of the test has not been reported.¹⁰ For example, in this cat a partial response to dilute phenylephrine suggested a postganglionic lesion. But at necropsy, the cat was found to have tumor metastasis involving the thoracic sympathetic trunk, with no evidence of postganglionic disease.

Pulmonary metastatic disease in dogs and cats typically appears as well-circumscribed, interstitial nodules. However, it has been suggested that cats are more likely to have an atypical pattern of metastasis on thoracic radiographs, and in one study, seven of 25 cats with pulmonary metastases showed a diffuse pattern; all had epithelial tumors, although none had transitional cell carcinoma.¹³ The cat described here developed a diffuse bronchial pattern that was seen on thoracic radiographs at Day 90 after surgery, and at necropsy the cat was found to have numerous small pulmonary metastases with no evidence of bronchial disease. CT provides additional information when compared with thoracic radiographs alone in both dogs and cats.^14,15 In this cat, the thoracic CT scan identified thoracic lymphadenopathy that was not evident on plain radiographs. Interestingly, the pulmonary parenchyma was interpreted as normal on the CT scan, which brings into question whether the bronchial change interpreted on plain radiographs represented the pulmonary metastases that were demonstrated postmortem.