Eosinophilic granulocytic sarcoma in a pig

A case of granulocytic sarcoma originating from an eosinophilic lineage is described in a 5-year-old, mixed-breed, female pig. The pig had been originally sent to slaughter in a good plane of nutrition and without displaying clinical disease. At gross examination, green masses were observed in several bones, especially vertebrae, sternum, pelvis, and long bones such as femur and humerus. Similar masses were seen in skeletal muscles, lymph nodes, and kidneys. Cytology revealed large numbers of round cells with round nuclei and scant cytoplasm (myelocytes); some of these cells had a fine eosinophilic granularity to their cytoplasm (eosinophil myelocytes). Histologically, the neoplastic cells formed sheets that completely obliterated the normal architecture of subperiosteal bone marrow. The cytoplasm of the neoplastic cells stained strongly by Sirius red stain of eosinophil and was positively marked by immunohistochemistry using an anti-myeloperoxidase antibody. The association of gross examination, cytology, histology, histochemistry, and immunohistochemistry findings is consistent with a diagnosis of eosinophilic granulocytic sarcoma.