Chronic Neutrophilic Leukemia in a Patient With Multiple Myeloma.

High-dose chemotherapy used for autologous stem cell transplantation (ASCT) is often associated with the proliferation of cells with neoplastic capabilities. As a result, expansion of one particular cell line, i.e., clonal hematopoiesis (CH), can occur. The frequency of CH in multiple myeloma (MM) has been reported as ~21.6%. Although neutrophilia in MM could be a leukemoid reaction, one should not forget hematologic neoplasms such as chronic neutrophilic leukemia (CNL) - which is characterized by CSF3R mutation, and absence of cytopenia and/or significant morphologic dyspoiesis. In this case report, we describe a 76-year-old female patient (currently 77 years old) who developed CNL 23 years after ASCT for MM and presented with a white blood cell (WBC) count of 71.2 K/µL.