Chronic neutrophilic leukemia (CNL) is a rare
myeloproliferative disorder characterized by sustained neutrophilic
leukocytosis and absence of the
Philadelphia chromosome. Most patients with CNL have normal karyotypes, and no specific
cytogenetic abnormality has been identified. We report here a patient with CNL that evolved to myeloid
blast crisis. A 73-year-old man was admitted to the hospital because of marked
leukocytosis (leukocyte count 112.5 x 10(9)/L with 91% segmented neutrophils) and massive hepatosplenomegaly that was diagnosed as CNL with a normal karyotype.
After treatment with
hydroxyurea for 7 months, the disease progressed to a
blast crisis. Bone marrow showed myeloid
hyperplasia with 21% myeloblasts, 15% promyelocytes, and marked dysplastic changes of neutrophils. Blastic cells were positive for CD10, CD13, CD14, CD33, CD34, and
HLA-DR. Chromosome analysis of the bone marrow cells showed 46,XY,+X in all 20 metaphase spreads. We reviewed 15 cases of CNL terminating in the
blast crisis and confirmed that all cases transformed into myeloid crises and had poor prognoses. Furthermore, to our knowledge, this is the first case showing the acquired gain of an extra X chromosome as a sole abnormality in CNL. The gain of an extra X chromosome may play an important role in the progression from chronic phase to the
blast crisis of CNL.