Pulmonary Histiocytic Sarcoma in Two Aged Dogs of a Beagle Colony

Pulmonary masses were observed in two aged Beagles maintained for a long period without any treatment. In the histopathology in both cases, the poorly demarked masses were composed of neoplastic cells proliferating in a sheet-like fashion within the alveolar lumen. These cells showed moderate to marked pleomorphism and atypia and had abundant eosinophilic to foamy cytoplasm. Phagocytosis and multinucleated giant cells were occasionally observed. Similar lesions with pulmonary infiltrates were not noted in any of the observed tissues in both cases. In the immunohistochemistry, the neoplastic cells were positive for vimentin, lysozyme and alpha-1-antitrypsin, but not for cytokeratin or lymphocytic markers such as CD3 or CD79a. The tumor cells also showed lectin binding affinities such as concanavalin A and ricinus communis agglutinin-1. These findings indicated that these neoplastic cells were derived from a histiocytic lineage. Therefore, we diagnosed them as pulmonary histiocytic sarcomas.