The recent discovery of mutations in the receptor for colony-stimulating factor 3 (CSF3R; GCSFR), a commercially available mutation of which 50–60% of patients with CNL have been reported to harbor [4], may improve our ability to determine the clonality of the neutrophils in CNL and help confirm or refute the coexistence of CNL and multiple myeloma as a real phenomenon. The gene discussed is CSF3R; the disease is chronic neutrophilic leukemia.