TO THE EDITOR:

Chronic neutrophilic leukemia (CNL) is a rare myeloproliferative neoplasm characterized by sustained mature neutrophil proliferation, bone marrow (BM) granulocytic hyperplasia, and splenomegaly. For a long time, the diagnosis of CNL has been based on the exclusion of genetic abnormalities that are known to occur in other myeloproliferative neoplasms. In 2013, the discovery of recurrent mutations in the CSF3R gene in the majority of patients with CNL has revolutionized the understanding of the pathogenesis of this disease and provided a biomarker for CNL diagnosis. Consequently, the World Health Organization revised the diagnostic criteria for CNL in 2016 to include CSF3R mutations (T618I or other activating CSF3R mutation).

The CSF3R gene encodes the colony-stimulating factor 3 receptor (also known as granulocyte colony–stimulating factor [G-CSF] receptor) which is critical for differentiation and proliferation of neutrophils. The structure...

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