Chronic Neutrophilic Leukemia: A Case Report of a Rare Myeloproliferative Neoplasm With a CSF3R Mutation.

Cases of chronic neutrophilic leukemia (CNL) are extremely rare and easily missed. The World Health Organization revised criteria in 2016 to include evaluation for CSF3R somatic mutations. In this article, we discuss an 84-year-old man who initially presented with leukocytosis, macrocytosis, and mild splenomegaly. The bone marrow biopsy and aspirate revealed hypercellularity (90%) and was comprised primarily of mature neutrophils. There was no genetic rearrangement of PDGFRA, PDGFRB, FGRF1, BCR-ABL, or JAK2. A skin biopsy of a hyperpigmented area on the palm of the patient's hand proved to be a neutrophilic infiltrate. This patient experience is presented to highlight several issues: the rarity of CNL, the role of molecular testing to confirm diagnosis, and the aggressive nature of this unusual myeloproliferative neoplasm.