Evidence for the clonal nature of hypereosinophilic syndrome

Hypereosinophilic syndrome (HES) is a disease process of unknown pathogenesis. Although some cases are believed to be primary hematologic malignancies, this issue remains unsolved. We present a case of HES in whom we have observed a clone of cytogenetically abnormal cells in the bone marrow in parallel with a clinical picture of a hematologic disorder characterized by progressive proliferation and organ infiltration by eosinophils. The cytogenetic abnormality 46,XY,t(7;12)(q11;p11) is previously unreported. Our case, plus other evidence present in the literature, supports the concept that HES is a hematologic malignant neoplasia.