LAUSR

The work‐up of patients with hypereosinophilia (HE) is complex. Following the recently revised World Health Organization criteria, we retrospectively reviewed 125 patients who were referred to us to exclude a neoplastic cause of HE (2003‐2016). The clinical laboratory work‐up confirmed secondary HE in 25 (20%) patients; myeloid/lymphoid neoplasms with rearrangements of PDGFRA (n = 9) or PDGFRB (n = 2) (9%); HE associated with a well‐defined myeloid neoplasm in 8 (6%); and abnormal bone marrow and/or molecular genetic abnormalities consistent with chronic eosinophilic leukemia (CEL), not otherwise specified (NOS) in 21 (17%) patients. For the remaining 60 (48%) patients, a specific diagnosis was not identified, and 56 patients had HE related findings consistent with idiopathic hypereosinophilic syndrome (HES), while 4 patients who were asymptomatic. With a median follow up of 35.3 months (range, <1‐104), patients with CEL, not otherwise specified (NOS) had a median OS of 26.1 months, significantly inferior to patients with idiopathic HES (not reached, P < .01). Thus, our experience in a single tertiary cancer center shows that the work‐up of HE following WHO recommendations requires a multimodality‐based approach; and a correct diagnosis determines risk stratification and proper patient management. However, the causes of HE remain unknown in approximately half of referred patients, indicating the need for further studies.