Introduction

This category was recently introduced by the WHO classification into the subgroup of myelodysplastic/myelopro-liferative disorders.1 To some extent, it is still a diagnosis of exclusion and includes patients with predominantly overproduction of neutrophils and various degrees of dysplasia in one or more hematopoietic lineages. The most important feature, differentiating aCML from CML is the absence of the BCR/ABL translocation or any variant translocations present in CML. This makes the diagnostic category of aCML similar, if not identical, to that of BCR/ABL-negative CML.56 Minor distinguishing features include absence of basophilia, older age, more frequent presentation with lower WBC counts, thrombocytopenia, and anemia.56-60 Separation from CMML is less stringent: Both disorders share the prolif-erative and dysplastic marrow feature, high median age, and a lack of distinguishing cytogenetic or molecular features. The presence of absolute monocytosis (>1x 109/L monocytes) in CMML in association with relative monocytosis (>8-10% monocytes on blood smear2 56 58 60) separates CMML from aCML. aCML is a rare disease, and in the past cases were included in the category of Ph- negative CML. As about one-half of Ph-negative CML cases are BCR/ABL positive,60 61 it was difficult to assess characteristic features, prognosis, and response to therapies. Assuming that BCR/ABL-negative cases of CML and aCML are, if not identical, then clinicopathologically very similar entities, information on characteristics, prognostic variables, and outcome of this rare disorder(s) can be based on an analysis of 76 patients.56 The median survival of patients was 24 months and progression into acute leukemia occurred in 30%. Chromosomal abnormalities were found in 30% of patients, with trisomy 8 being the most frequent, while monosomy 7 was not observed. Complex chromosomal abnormalities were rare. Multivariate analysis identified age >65 years, hemoglobin <10 g/dL, and WBC >50 X 109/L as variables associated with poor survival. Younger patients with better blood counts had a median survival of 38 months, compared to 9 months for older patients with compromised counts.56 The overall prognosis is worse and survival shorter in patients with a CML (Bcr/Abl-negative CML) compared to Ph'-positive CML.58 5961 In at least one study, the survival seems not significantly affected by treatment.56

The outcome is, however, similar to that in CMML.3'4'56'59'61 No study has demonstrated the importance of the single objective distinguishing feature of monocytosis as being associated with a different outcome. A detailed analysis of factors associated with outcome in 485 patients (CMML, 304; BCR/ABL-nega-tive CML, 74; Ph-negative, BCR/ABL unknown, 107) found that a diagnosis of CMML indeed confers a significantly shorter median survival (12.6 months) than BCR/ABL-negative CML [21.4 months and Ph-negative, BCR/ABL unknown CML (18.3 months)]. This finding provided, for the first time, the empirical support for separating aCML from CMML.45

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