Early relapse of JAK2 V617F-positive chronic neutrophilic leukemia with central nervous system infiltration after unrelated bone marrow transplantation.

Chronic neutrophilic leukemia (CNL) is a rare myeloproliferative disorder characterized by a proliferation mainly of mature neutrophils. The prognosis is generally poor and an optimal therapeutic strategy remains to be determined. Allogeneic hematopoietic stem cell transplantation (HSCT) is expected to be the only curative therapy so far. We report a 46-year-old male with progressive CNL who underwent bone marrow transplantation from an HLA-matched unrelated donor. After engraftment was achieved on day 35, relapse of CNL was confirmed on day 50. The progression of CNL was very rapid afterward and infiltration to the central nervous system was observed. The Janus Kinase 2 (JAK2) V617F homozygous mutation was detected from the peripheral blood or bone marrow samples throughout the clinical course. From comparison with reports of successful HSCT for CNL in the literature, it was inferred that HSCT should be performed in a stable status before progression. Furthermore, JAK2 V617F-positive CNL may contain an aggressive disease entity in contrast to previous reports. Accumulation of experiences is required to establish a definite role of HSCT in the treatment of CNL and a prognostic significance of JAK2 mutation in CNL.