Chronic neutrophilic leukaemia (CNL) is a rare Philadelphia-negative BCR-ABL1-negative haematological neoplasm characterized by neutrophilia without any increase in eosinophils or basophils and with only low numbers of circulating granulocyte precursors. It is categorized in the World Health Organization (WHO) classification as one of the myeloproliferative neoplasms [1, 2].
There is usually splenomegaly and often hepatomegaly as well. Around a quarter of patients have gastrointestinal or other mucosal bleeding. Pruritus and gout can also occur.
Haematological and pathological features
There is usually leucocytosis and neutrophilia (Fig. 4.1). The WHO diagnostic criteria require a white blood cell count (WBC) of at least 25 × 109/l, with more than 80% of cells being neutrophils, granulocyte precursors being less than 10%, and circulating blasts less than 1%. Neutrophils are not dysplastic but may show toxic granulation. Anaemia and thrombocytopenia are late features.
Peripheral blood film in chronic neutrophilic leukaemia showing an increase of mature neutrophils that do not have dysplastic features. May-Grünwald-Giemsa stain, high power.
The bone marrow is hypercellular as a result of increased granulopoiesis. Myeloblasts are less than 5% and maturation is normal. No lineage shows dysplasia. Trephine biopsy sections shows hypercellularity due to increased granulopoiesis. Reticulin is usually normal. Splenic infiltration is mainly in the red pulp. Hepatic infiltration may be in sinusoids or portal areas.
As the disease progresses, dysplastic neutrophils and refractory leucocytosis can occur. Blast transformation occurs in up to 20% of patients [3, 4].
The immunophenotype is not relevant to diagnosis.
Cytogenetic and molecular genetic abnormalities
There is no specific cytogenetic or molecular genetic abnormality. By definition, t(9;22)(q34;q11.2) and the BCR-ABL1 fusion gene are absent. The karyotype is normal in about 90% of patients. Recurrent abnormalities reported in patients with an abnormal karyotype include del(11q), del(12p) and del(20q). Other abnormalities have included trisomy 8, trisomy 9, trisomy 21, del(3)(q21) and a complex karyotype. The JAK2 V617F mutation is occasionally present.
Diagnosis and differential diagnosis
It is important to exclude reactive neutrophilia, which can be marked and sustained in patients with a non-haematological neoplasm or with multiple myeloma or monoclonal gammopathy of undetermined significance. It is also important to make a distinction from the rare neutrophilic variant of chronic myelogenous leukaemia, which is associated with a 230 kDa BCR-ABL1 protein, rather than the usual 210 kDa protein. Pre-fibrotic primary myelofibrosis also needs to be distinguished - the presence of dysplastic features in myelofibrosis is useful in making this distinction.
The prognosis is variable but with a median survival of 23.5 ...