Variants of CML

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There are several disease entities that resemble CML but lack the Philadelphia chromosome or molecular evidence for bcr-abl translocation. Patients who are Philadelphia chromosome negative, but bcr-abl translocation positive appear to have a similar natural history to those who are Philadelphia chromosome positive.102 The term chronic neutrophilic leukemia, sometimes characterized as Philadelphia-negative CML, has been used to describe those with an elevated white count with a majority of mature neutrophils with no evidence of a Philadelphia translocation.103 A variant t(9;22) detectable only by molecular methods has recently been described in such patients.104 It is very important to rule out a leukemoid reaction, especially when an abdominal mass is present that may simulate splenomegaly.

Chronic eosinophilic leukemia, characterized by eosinophilic leukocytosis, the presence of immature eosinophils and myeloblasts, anemia, thrombocytopenia, or thrombocytosis may exhibit cytogenetic abnormalities other than the Philadelphia chromosome.105 Hepatosplenomegaly lymphadenopathy, and male predominance (77 percent) have been noted in this entity, which carries a poor prognosis. It is important to distinguish chronic eosinophilic leukemia from the idiopathic hyper-eosinophilic syndrome as well as reactive eosinophilic leuke-moid reactions (e.g., caused by underlying cancer or parasitic infection).106 Eosinophilic leukemia may present as a chronic myeloproliferative disorder sharing many features of CML, including terminal blast crisis.107 Eosinophilia and lymphoblastic lymphoma may coexist in patients with a t(8;13), which represents a rearrangement of the fibroblast growth factor gene.108

Chronic myelomonocytic leukemia (CMML)8-10 is characterized by splenomegaly, anemia, thrombocytopenia, leukocytosis (including monocyte and granulocyte cells in all stages of development) and increased blood and urine lysozyme levels. The FAB classification system considers CMML as a myelodysplastic syndrome characterized by the presence of monocytosis (greater than 1000 X 109/L) and myelodysplastic features in the bone marrow that cannot be infiltrated with greater than 20 to 30 percent blasts. The WHO proposal classifies CMML as an overlap syndrome between MDS and MPD5 (Table 3-1).

Juvenile chronic myelocytic leukemia (JCML) is a rare childhood malignancy characterized by leukocytosis, monocytosis, anemia with ineffective erythropoiesis, hepatosplenomegaly, marrow myeloid hyperplasia with less than 50 percent blasts, and the absence of the Philadelphia chromosome. Cells from patients with JCML seem to be exquisitely sensitive to granulo-cyte-macrophage colony-stimulating factor (GM-CSF),109 which suggests a primary pathogenic role for autocrine or paracrine growth factor stimulation as the primary etiologic event in this syndrome. This condition is a clonal disorder110 that can respond to retinoic acid.111

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