Spontaneous Disseminated Histiocytic Sarcoma in a Bengal Tiger (Panthera tigris tigris)

A 16-year-old, female, captive Bengal tiger (Panthera tigris tigris) had a history of a recurrent subcutaneous mass. After two attempts at surgical removal, euthanasia was elected during the third surgical attempt due to the degree of neoplastic infiltration. At necropsy, a large subcutaneous mass infiltrated the dermis, subcutis and abdominal wall with metastasis to the lungs, spleen and adrenal glands. Microscopically, the neoplasm formed nodules comprising sheets of round cells with large irregular nuclei. Toluidine blue and Giemsa stains were negative. An immunohistochemistry panel revealed membranous and cytoplasmic labelling with ionized calcium-binding adaptor molecule 1 (IBA1), cytoplasmic labelling with vimentin but no labelling with multiple myeloma oncogene 1 (MUM1), CD20 or pancytokeratin markers. Based on the gross distribution and histological and immunohistochemistry features, a diagnosis of disseminated histiocytic sarcoma was made. To the best of our knowledge, this is the first record of disseminated histiocytic sarcoma in a captive Bengal tiger.