Marked paraneoplastic hypereosinophilia associated with a low-grade, metastatic canine mast cell tumour

An 11-year-old, female, spayed labrador retriever was presented to the Iowa State University Oncology Service for evaluation of a rapidly expanding mass located near the right prescapular lymph node. A Patnaik grade I mast cell tumour (mitotic index 3  cells/µl, reference interval 0–0.75). The patient was diagnosed with a histologically low-grade, biologically high-grade cutaneous, metastatic mast cell tumour with paraneoplastic hypereosinophilia. Changes in the magnitude of peripheral hypereosinophilia frequently paralleled tumour response to treatment with multiple antineoplastic agents. Nine months after initiating chemotherapy, treatment was discontinued due to declining quality of life.