Primary pancreatic histiocytic sarcoma with peritoneal sarcomatosis in a cat

A 12-year-old neutered male Domestic Shorthair Cat, negative for feline immunodeficiency virus and feline leukaemia virus, was presented to the veterinary hospital with a 3-week history of anorexia, lethargy, abdominal pain and intermittent vomiting. Abdominal ultrasonography revealed a heterogeneous, poorly demarcated mass in the right mesogastric region, involving the pancreas and adjacent organs. Cytological evaluation of the abdominal fluid revealed a neoplastic effusion consistent with carcinomatosis. Given the poor prognosis, the cat was euthanized and submitted for necropsy, which revealed a large volume of free transudate within the abdominal cavity. In the pancreas, there was a 6.0 × 3.0 × 7.5 cm, irregular, soft, white-to-yellow mass and multiple small, firm, white nodules, ranging from 0.1 cm to 1 cm in diameter, were adhered to the omentum, mesentery, diaphragm and abdominal wall and to the serosal surfaces of the urinary bladder, intestines, spleen, stomach, liver and lungs. Microscopically, the pancreas contained a neoplastic proliferation composed predominantly of round cells arranged in loosely cohesive groups. Similar neoplastic proliferations were observed in the peritoneum, diaphragm, omentum and mesentery, the serosal surfaces of the urinary bladder, intestines, spleen, stomach, liver, left adrenal gland and lungs, and in the mediastinal lymph nodes. Based on these findings, the histopathological diagnosis was metastatic undifferentiated pancreatic neoplasia. Immunohistochemical evaluation revealed strong, diffuse cytoplasmic immunolabelling for vimentin and ionized calcium-binding adaptor molecule 1 in the neoplastic cells, with no labelling for pancytokeratin (AE1/AE3), E-cadherin, CD3 and CD20. The gross, histological and immunohistochemical findings were consistent with a histiocytic sarcoma of probable pancreatic origin, with metastatic dissemination throughout the peritoneum resembling that observed in primary pancreatic carcinomatosis. Histiocytic proliferative disorders are rare in cats, and the unusual presentation of this case provides an important contribution to the recognition of the possible manifestations of histiocytic sarcomas in this species.