Hemophagocytic histiocytic sarcoma of domestic animals

Background: Hemophagocytic histiocytic sarcoma is a unique, rare and highly malignant tumor of bone marrow and spleen macrophages. The marked erythrophagocytic activity of the neoplastic cells leads to a characteristic clinicopathological appearance and due to the frequent lack of mass formation, it has to be differentiated from immune-mediated disorders, mainly Evans syndrome. Objectives: The authors aimed to provide an overview of the tumor using scientific literature data and demonstrate the distinctive pathological lesions using their own cases. Materials and Methods: The carcass of a 5-year-old female Bernese Mountain Dog was brought to the Department of Pathology of the University of Veterinary Medicine for diagnostic necropsy, and also the biopsy samples of a 13-year-old, male Rottweiler dog for histological examination. Routine and special staining procedures were applied for the evaluation of characteristic histopathological lesions. Results and Discussion: These dogs showed a rapid course of illness, had hepatosplenomegaly, and the clinical case also presented the characteristic regenerative anemia and thrombocytopenia. With histopathological examination, the neoplastic macrophage infiltration could be seen in various organs, but mainly in the spleen and liver. The tumor cells showed marked erythrophagocytosis. This literature review supplemented with case presentations highlights the importance of hemophagocytic histiocytic sarcoma in the differentials of regenerative anemia and thrombocytopenia of domestic animals.