Sarcomatoid renal cell carcinoma in a binturong (Arctictis binturong).

An adult, female binturong (Arctictis binturong) was examined due to lethargy, inappetence, and an abdominal mass. Diagnostic investigations, including radiographs, abdominal ultrasound, clinical laboratory findings, and a fine-needle aspirate of the mass, were suggestive of a sarcoma with metastasis. Necropsy and histopathologic findings confirmed a widely disseminated sarcomatoid variant of a renal cell carcinoma, likely originating in the left kidney, with metastasis to the right kidney, spleen, pancreas, liver, mesenteric lymph nodes, and lungs. This is the first report of this neoplasm in a binturong and only the second report in the veterinary literature. Sarcomatoid renal cell carcinoma is a rare histologic variant of renal cell carcinoma that is aggressive, commonly metastatic, and associated with a very poor prognosis in humans. Accurate antemortem diagnosis of this tumor may be complicated by its biphasic morphology, which may resemble carcinoma or sarcoma (or both), often necessitating the use of immunohistochemical techniques.