Veterinary pathologists in Spain have documented what they believe is the first reported case of a primary pulmonary myxoid liposarcoma in a dog, an exceptionally rare fatty-tissue cancer arising within the lung itself. The case, published as an open-access case report in BMC Veterinary Research on 21 October 2026, describes an 11-year-old neutered male Beagle that had suffered a chronic cough and exercise intolerance for six months before diagnosis. The report emphasizes not the treatment outcome but the diagnostic workup: the authors argue that only by integrating cytology, computed tomography, histochemistry, histopathology and immunohistochemistry could the tumor be distinguished from other primary pulmonary mesenchymal tumors and from metastatic disease.
The diagnostic journey began with fine-needle aspiration cytology, which yielded a sparsely cellular sample containing spindle-shaped mesenchymal cells with prominent cytoplasmic vacuolation, abundant extracellular lipid droplets, and numerous lipid-laden macrophages. That combination raised initial suspicion of lipogenic differentiation — in other words, that the tumor cells were producing fat — but cytology alone could not settle the question, because lipid-laden macrophages can mimic fat-producing tumor cells under the microscope.
Computed tomography then 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 and caused marked local mass effect. Critically for staging, it was not associated with regional lymphadenopathy or distant metastatic disease, which supported the possibility that the lung was the primary site rather than a waypoint for a cancer that had spread from elsewhere in the body.
Following surgical lobectomy, histopathological examination showed a predominantly hypocellular myxoid neoplasm: sparse spindle to ovoid cells embedded in an abundant myxoid stroma that stained positively with Alcian blue, interspersed with mature adipocytes. Scattered vacuolated cells stained with Sudan IV confirmed intracellular lipid, but the authors note a key limitation — those cells could not always be unequivocally distinguished from lipid-laden macrophages, a recurring diagnostic pitfall in liposarcoma pathology.
Immunohistochemistry helped resolve the cellular identity questions. The neoplastic cells showed diffuse vimentin expression, a marker of mesenchymal origin, and variable S100B immunoreactivity, which is consistent with lipogenic tumors. They showed no immunolabeling for Iba1 or α-smooth muscle actin, excluding a macrophage or smooth-muscle origin for the tumor cells themselves. Iba1 instead highlighted a distinct population of tumor-associated macrophages, some of which were lipid-laden — explaining the cytological mimicry that had complicated the initial aspiration sample.
Proliferative activity appeared relatively low. The tumor showed a low mitotic count and a Ki67 labelling index of 9.94%, a measure of the fraction of cells in active cell division. Integration of all findings — cytological, imaging, histochemical, histopathological and immunohistochemical — supported the final diagnosis of primary pulmonary myxoid liposarcoma.
The clinical follow-up, though limited, was favorable: the dog remained clinically healthy, with no evidence of local recurrence or metastatic disease at approximately 11 months after surgery. The authors are careful, however, not to generalize from a single animal. Their conclusions state that additional well-documented cases with long-term follow-up are needed to better characterize the biological behavior and prognostic features of this neoplasm, which remains so rare in veterinary medicine that a single case constitutes the entire documented canine record of a primary pulmonary origin.
Background provided in the report notes that while liposarcomas have occasionally been reported within the thoracic cavity of dogs, a pulmonary origin has rarely been documented, making this case a first to the authors’ knowledge. The report’s broader significance lies in its methodological message: for rare mesenchymal tumors of the lung, no single test is sufficient, and distinguishing myxoid liposarcoma from other primary pulmonary mesenchymal tumors — and from metastatic disease — requires the deliberate combination of imaging, staining and immunophenotyping described in this case.
Subject of Research: First reported case of primary pulmonary myxoid liposarcoma in a dog, diagnosed through integrated cytology, imaging, histochemistry and immunohistochemistry.
Article Title: Primary pulmonary myxoid liposarcoma in a dog
Article References: Criado, M., Zapico, D., Mendívil, P., Millán-Varela, L., Prada, I., Álvarez-Villaverde, M., Ferreras, M. C., Benavides, J., & Espinosa, J. (2026). Primary pulmonary myxoid liposarcoma in a dog. BMC Veterinary Research. https://doi.org/10.1186/s12917-026-06035-0
Image Credits: AI Generated
DOI: 10.1186/s12917-026-06035-0
Keywords: veterinary pathology, dog, liposarcoma, pulmonary tumor, myxoid neoplasm, immunohistochemistry, computed tomography, case report, oncology, Beagle, Ki67, diagnostic imaging
News Source: William Thompson. (October 30, 2026). Rare Lung Tumor in a Dog Identified as First Canine Primary Myxoid Liposarcoma. Scienmag.
