Is hypereosinophilic syndrome a malignant disease?

A patient with an abdominal mass for 4 years developed hypereosinophilia and weight loss. Bone marrow aspirations and biopsy specimens showed hypercellularity of eosinophils. No cause for hypereosinophilia was found. Biopsy specimens of several organs, including the abdominal mass, showed eosinophilic infiltration with reactive fibrosis in some. Cytogenetic studies of the bone marrow before treatment with cytoxic drugs showed chromosomal abnormalities. Several of these have been reported in association with acute or eosinophilic leukemias. Based upon these findings, the authors believe that the patient had eosinophilic leukemia and that the abdominal mass probably was an eosinophilic chloroma.