Primary cardiac histiocytic sarcoma in a dog

An intact male mixed-breed dog was presented with anorexia and depression. Ultrasonographic examination did not reveal any nodules in the thoracic or abdominal organs. However, several nodules of different sizes were identified in the heart at necropsy, with no gross lesions detected in other organs. Histological examination of the cardiac tissues revealed an accumulation of pleomorphic, round-to-oval phagocytic cells, suggestive of histiocytic origin, which was subsequently confirmed by immunohistochemistry with specific histiocytic antibodies (Iba1 and HLA-DR). Although no gross nodules were observed in the lungs, histologic examination revealed scattered neoplastic cells, indicating metastasis from the primary cardiac lesion. This case represents a rare pathological presentation of primary cardiac histiocytic sarcoma in a dog, expanding the documented anatomical and pathological spectrum of canine histiocytic sarcoma.