Liposarcoma is a malignant and rare tumor of lipocytes in domestic animals. This tumor typically involves the subcutis of extremities and the trunk in dogs, although it may arise in other anatomic sites, including spleen, bone, extradural spine, liver, heart, lung, thorax, and bone marrow. Liposarcomas are usually locally invasive but have a low metastatic rate and lung, liver, spleen, and lymph node are the most common sites for metastases of the tumor. An 1.5-year-old, Shih tzu dog with a history of anorexia, listlessness, emaciation, fever, alternative nausea and polydipsia was referred to a private small animal clinic in Mashhad due to presence of a globular mass in the subcutaneous of thoracic region. The mass, 5cm in diameter, had irregular margins. After surgical removal, the tumor had yellow color and soft texture and for histopathological study, was sent to Department of Pathology, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad. After fixation of the specimens in buffered formalin solution and tissue processing through routine paraffin embedding technique, they were cut at 5 μm and stained with hematoxylin and eosin. Microscopically, some neoplastic cells were differentiated to adipocytes and there were a lot of pleomorphic tumor cells among the adipocytes. The pleomorphic neoplastic cells had nuclei with different shapes and sizes, various degrees of nuclear chromasia and prominent nucleoli and the cytoplasm was vacuolar. Tumor giant cells with multiple hyperchrome nuclei and also mitotic figures were observed in some sections. Based on macroscopic and microscopic characteristics, the mass was diagnosed as pleomorphic liposarcoma and to the authors, knowledge, there is no report from Iran about the occurrence of this histopathologic subtype of the tumor.

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