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A 7-year-old intact female domestic medium hair cat was examined at a veterinary clinic for a scabbed nodule over the right shoulder. Multiple nodules recurred at the same site after the first surgical excision, and a second surgical excision was performed. Histopathology demonstrated high-mitotic-rate neoplastic cells and therefore a histiocytic proliferative disease was initially suspected. The condition progressed rapidly within a 5-month period and the cat was euthanized due to sudden onset of severe dyspnea. Necropsy showed diffuse metastatic nodules in the lungs, confirming a histiocytic proliferative disease, with histiocytic sarcoma being the most likely differential diagnosis., (Copyright and/or publishing rights held by the Canadian Veterinary Medical Association.)

A 9-year-old spayed female domestic shorthair cat presented with a skin lesion of the left tarsus. The lesion was biopsied and, based on the microscopic appearance and immunohistochemical characteristics, histiocytic sarcoma was diagnosed. Amputation was performed with improved demeanor seen postoperatively. However, between 44 and 60 days following the surgery, relapse of skin lesions appeared in multiple locations, including at the previous amputation site, and euthanasia was elected. This is the first report of a histiocytic sarcoma treated with amputation in a cat.

Case Description: An 11-year-old neutered female domestic longhair cat was evaluated because of a 1-week history of progressive dyspnea, signs of depression, and loss of appetite. A histiocytic sarcoma had been excised from the mammary gland 6 weeks earlier., Clinical Findings: Physical examination findings were consistent with pleural effusion, and thoracic and abdominal radiography and ultrasonography revealed pleural effusion, a thoracic mass involving the aorta and pulmonary artery, and a caudal abdominal mass that most likely represented enlarged iliac lymph nodes. Cytologic examination of the pleural fluid and fine-needle aspirates from the iliac and right popliteal lymph nodes revealed abundant cells with neoplastic characteristics of indeterminate origin. The clinical diagnosis was generalized malignant neoplasia., Treatment and Outcome: Pleural drainage was necessary every 5 to 6 days. Exploratory thoracotomy and biopsy of the mass were recommended for better characterization of the thoracic disease. Simultaneously, palliative treatment by advancement of the omentum into the thorax was performed. A final diagnosis of disseminated histiocytic sarcoma was made, and treatment with doxorubicin was begun after surgery. During the 13 months after surgery, the cat was free from signs of respiratory tract disease and had normal activity levels with good exercise tolerance. Fifteen months after surgery, the cat's clinical condition worsened and the cat died., Clinical Relevance: Findings suggested that thoracic omentalization may be considered for palliative treatment of cats with refractory neoplastic pleural effusion when frequent thoracocentesis is necessary and other treatments are not suitable.