Chronic myeloid leukaemia supervening in myeloproliferative neoplasms
The haematological features of chronic myeloid leukaemia can occur as a feature of disease evolution in polycythaemia vera, essential thrombocythaemia and primary myelofibrosis (Fig. 8.1). The blood film can resemble that of chronic myelogenous leukaemia (CML), chronic myelomonocytic leukaemia (CMML), atypical chronic myeloid leukaemia (aCML) or, occasionally, chronic neutrophilic leukaemia (CNL) . There may be progression to blast transformation.
Chronic myeloid leukaemia supervening in primary myelofibrosis. The peripheral blood film shows marked leucocytosis, with an increase of neutrophils and mature and immature monocytes. One nucleated red blood cell is present and there are multiple Howell-Jolly bodies as a result of previous splenectomy.
Chronic basophilic leukaemia
Chronic myeloid leukaemia with prominent basophilia is often actually CML, sometimes in accelerated phase and, when BCR-ABL1-positive, should be classified and treated as CML. Chronic basophilic leukaemia has also been observed in two patients with a PRKG2-PDGFRB fusion gene [2, 3]. In one patient there was splenomegaly, a white blood cell count (WBC) of 34 × 109/l with 20–40% basophils, bone marrow fibrosis, megakaryocyte dysplasia, increased abnormal mast cells in the bone marrow and elevated serum tryptase, associated with t(4;5;5)(q23;q31;q33) . In the other there was splenomegaly, a WBC of 26.3 × 109/l with 26% basophils, abnormal bone marrow mast cells and increased serum tryptase associated with t(4;5)(q21.1;q31.3) . Such cases should be assigned to the World Health Organization (WHO) category of lymphoid or myeloid neoplasm with rearrangement of PDGFRB, and should be treated with imatinib or another tyrosine kinase inhibitor.
Cases of chronic myeloid leukaemia with dominant basophilia and no BCR-ABL1 or PDGFRB rearrangement should be recognized as chronic basophilic leukaemia. There may be splenomegaly and some patients have symptoms due to histamine excess.
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