Mast cell tumor with eosinophilic phagocytosis in a dog

Abstract

A 14-year-old castrated male Shiba dog presented with a 6 cm-diameter mass in the left cervical lymph node. Histopathologically, the mass consisted of sheets of neoplastic mast cells and diffuse eosinophils. The neoplastic cells exhibited marked atypia including anisocytosis, a high mitotic index, karyomegaly and multinucleation. Some neoplastic cells had phagocytosis of 1–7 eosinophils in the cytoplasm. Immunohistochemistry revealed that the neoplastic cells were positive for anti c-kit antibody, and based on the above findings, a mast cell tumor was diagnosed. Eosinophils were observed in the cytoplasm of the tumor cells by double staining with Luna stain and immunostaining for anti c-kit antibody.