Primary pulmonary myxoid liposarcoma in a dog

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Primary pulmonary liposarcoma is an exceptionally rare neoplasm in veterinary medicine. Although liposarcomas have occasionally been reported within the thoracic cavity of dogs, a pulmonary origin has rarely been documented. This report describes the clinicopathological, histochemical, and immunohistochemical features of, to the authors’ knowledge, the first reported case of primary pulmonary myxoid liposarcoma in a dog. Particular emphasis was placed on the diagnostic approach and differential diagnoses required to distinguish this neoplasm from other primary pulmonary mesenchymal tumors. An 11-year-old neutered male Beagle was presented with a six-month history of chronic cough and exercise intolerance. Fine-needle aspiration cytology yielded a sparsely cellular sample containing spindle-shaped mesenchymal cells with prominent cytoplasmic vacuolation, abundant extracellular lipid droplets, and numerous lipid-laden macrophages, raising suspicion of lipogenic differentiation. Computed tomography revealed a large, well-circumscribed pulmonary mass composed predominantly of macroscopic fat, with mild enhancement of a thin peripheral rim and scattered internal soft-tissue components. The mass arose from the right middle lung lobe, caused marked local mass effect, and was not associated with regional lymphadenopathy or distant metastatic disease. Following surgical lobectomy, histopathological examination revealed a predominantly hypocellular myxoid neoplasm composed of spindle to ovoid cells embedded in abundant Alcian blue-positive myxoid stroma, interspersed with mature adipocytes. Scattered Sudan IV-positive vacuolated cells contained intracellular lipid but could not always be unequivocally distinguished from lipid-laden macrophages. Neoplastic cells showed diffuse vimentin expression, variable S100B immunoreactivity, and no immunolabeling for Iba1 or α-smooth muscle actin. Iba1 instead identified a distinct population of tumor-associated macrophages, some of which were lipid-laden. The neoplasm showed a low mitotic count and a Ki67 labelling index of 9.94%, indicating relatively low proliferative activity. Integration of the cytological, imaging, histochemical, histopathological, and immunohistochemical findings supported a diagnosis of primary pulmonary myxoid liposarcoma. The dog remained clinically healthy, with no evidence of local recurrence or metastatic disease at approximately 11 months after surgery. This report represents the first documented case of primary pulmonary myxoid liposarcoma in a dog. It highlights the importance of integrating cytology, computed tomography, histopathology, histochemistry, and immunohistochemistry in the diagnosis of this exceptionally rare neoplasm and in its distinction from other primary pulmonary mesenchymal tumors and metastatic. Additional well-documented cases with long-term follow-up are needed to better characterize the biological behavior, prognostic features.