Soft tissue sarcoma mimicking eosinophilic leukemia.

Blood eosinophilia is diagnosed by an absolute eosinophil count that exceeds 0.5 × 109/L.1 Hypereosinophilia is classified as either primary, due to clonal expansion of eosinophils through acquisition of a somatic mutation (eg, FIP1L1-PDGFRA),1 or secondary, as seen in response to exogenous type 2 cytokines (eg, IL-3, IL-5, and GMCSF) secreted by various cells (eg, T-lymphocytes).2-4 Secondary eosinophilia is seen in a variety of conditions, such as parasitic infestations, drug reactions, allergic reactions, connective tissue disorders, vasculitis, endocrinopathies, and malignancy.5 Rarely, secondary eosinophilia may be associated with pulmonary infections, eosinophilic gastroenteritis, and autoimmune diseases. Hypereosinophilia is present in less than 1% of patients at the time of diagnosis of malignancies such as lymphomas, leukemias, soft tissue sarcomas, lung cancer, cervical cancer, gastrointestinal cancer, renal cancer, and breast cancer. Hypereosinophilia may be a paraneoplastic manifestation of these malignancies.6 Hypereosinophilic syndrome (HES) comprises a group of myeloproliferative disorders of unknown etiology that are marked by a sustained overproduction of eosinophils. HES is characterized not only by a striking and sometimes profound eosinophilia associated with the syndrome, but also by end-organ damage, most commonly involving the heart, with the development of eosinophilic endomyocardial fibrosis. The currently defined criteria for HES are: persistent eosinophilia of greater than 1,500 eosinophils/mm3 for more than 6 months; exclusion of other potential etiologies for the eosinophilia, including parasitic, allergic, or other causes; and signs and symptoms of organ system dysfunction or involvement that appear to be related to the eosinophilia.7,8