Cytologic identification of erythrophagocytic neoplasms in dogs

Background: Erythrophagia has been identified in multiple types of tumors in human medicine, but information in veterinary medicine is limited. In dogs and cats, erythrophagia has been reported to occur in mast cell and plasma cell tumors, lymphoma, megakaryocytic leukemia, and hemophagocytic histiocytic sarcoma. On the basis of clinical experience, we believed this to be an incomplete list that might bias veterinarians toward a diagnosis of histiocytic sarcoma when erythrophagia is observed in neoplastic spindle-shaped cells. Objective: The objective of this retrospective study was to identify neoplasms in dogs that exhibit erythrophagia within the neoplastic cell population. Methods: Reports of cytologic samples collected from dogs and submitted to the University of Illinois Veterinary Diagnostic Laboratory between January 2003 and May 2011 were searched for a description of erythrophagia. Only cases with a diagnosis confirmed by histopathologic examination using immunohistochemical analysis or by cytochemical staining were included. Slides were reviewed by one pathologist to confirm the presence of erythrophagocytic neoplastic cells. Results: Of 20,016 reports searched, 897 contained the term "erythrophagia." In 55 reports, neoplastic cells exhibiting erythrophagia were identified. Of these, 21 cases were excluded because the cytologic diagnosis was not confirmed, and the remaining 34 cases included 12 hemangiosarcomas, 11 hemophagocytic histiocytic sarcomas, 9 osteosarcomas, one mast cell tumor, and one T-cell lymphoma. Conclusion: Erythrophagia can be found in many tumor types. When erythrophagia is observed in spindle-cell sarcomas, osteosarcoma and hemangiosarcoma should be considered in addition to hemophagocytic histiocytic sarcoma.