Chronic Eosinophilic Leukemia Not Otherwise Specified: A Case Series

Chronic eosinophilic leukemia (CEL) is a rare myeloproliferative neoplasm characterized by sustained elevation of eosinophil counts greater than > 1.5 × 10⁹/L in blood or bone marrow. Approximately 25-30% of patients with persistent hypereosinophilia have somatic mutations associated with myeloid neoplasms, and next generation sequencing has led to the use of newer treatments for CEL, including tyrosine kinase inhibitors (TKIs) such as imatinib. Before the advent of imatinib, the disease had a poor prognosis with a 5-year mortality close to 50%. However, in patients with CEL without the characteristic mutations, known as chronic eosinophilic leukemia, not otherwise specified (CEL-NOS), treatment options and guidance are limited. We present a case series of two CEL-NOS patients treated at our academic health sciences center.