Severe paraneoplastic hypereosinophilia in metastatic renal cell carcinoma

A 46 year-old patient patient with a history of significant weight loss, reduced general state of health and coughing underwent radical nephrectomy for metastasized renal cell carcinoma. Three weeks after surgery, the patient presented with excessive peripheral hypereosinophilia leading to profound neurological symptoms due to cerebral microinfarction. Systemic treatment with prednisolone, hydroxyurea, vincristine, cytarabine, temsirolimus and sunitinib led to reduction of peripheral eosinophils but could not prevent rapid disease progression of the patient. At time of severe leukocytosis, a considerable increase of cytokines associated with hypereosinophilia was measurable.Paraneoplastic hypereosinophilia in patients with renal cell carcinoma might indicate poor prognosis and rapid disease progression. Myelosuppressive therapy is required in symptomatic patients.Renal cell carcinoma can cause various paraneoplastic syndromes such as hypercalcemia, hypertension and ectopic hormone production [1]. Renal cell carcinoma can also provoke hematologic disturbances such as polycythemia due to an increased production of erythropoietin [2]. Hypereosinophilia has been reported as a paraneoplastic syndrome in several solid and hematological malignancies. We report the first case of severe paraneoplastic hypereosinophilia with cerebral infarction in a patient with metastatic renal cell carcinoma.A 46 year-old patient with no relevant diseases in past medical history had a history of significant weight loss, reduced general state of health and coughing. A whole body CT revealed a hypervascularized renal tumor with a level I tumor thrombus [3] (Figure 1) and multiple pulmonary lesions. At the time of primary diagnosis, blood analysis showed a WBC of 19,550/μl (4,000-7,000/μl) with 16% (0-6%) of eosinophilic granulocytes. The patient was admitted to our hospital 7 days after primary diagnosis (day 7) for radical nephrectomy, partial hepatectomy and reconstruction of the inferior v