Presence of the JAK2 V617F mutation in a patient with chronic neutrophilic leukemia and effective response to interferon α-2b.

Chronic neutrophilic leukemia (CNL) is a rare type of leukemia characterized by a proliferation mainly of mature neutrophils, elevated neutrophil-alkaline phosphatase activity, and no presence of the Philadelphia chromosome. The prognosis is generally poor and there is no consensus therapeutic strategy for the treatment of this disease. The JAK2 V617F mutation has been detected in patients with classical myeloproliferative disorders (MPD) including polycythemia vera and essential thrombocythemia and idiopathic myelofibrosis. In contrast, this same mutation has been detected in only 4 patients with CNL to date, suggesting that the JAK2 V617F mutation is a rare event in patients with atypical MPD. Here, we report a case of CNL with presence of the JAK2 V617F mutation. After treatment with interferon alfa-2b with 3 million units every other day for 1 month, the patient's white blood cell count was well controlled below 10.0 ×10⁹/l. At present, our patient remains symptomatically well and is maintained on interferon alfa-2b (3 million units twice a week), and his neutrophil count now averages around 8.0-10.0 ×10⁹/l.