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CORRESPONDENCE The recent review article by Vardiman et al on the World Health
Organization (WHO) classification of myeloid neoplasms1 described the diagnostic criteria for acute erythroleukemia. Of particular interest to us is the description of acute erythroid/myeloid leukemia. According to the WHO,2 acute erythroid/myeloid
leukemia is defined as having at least 50% erythroid precursors in the entire marrow nucleated cell population and myeloblasts that account for at least 20% of the nonerythroid cell (NEC) population. We recently have seen in our hospital/consultation service 5 patients (Table
1) with bone marrow aspirates revealing 4%-11.6% myeloblasts and
erythroid precursors comprising 58.2%-83.6% of the nucleated cells
within the marrow, based on a 500-cell differential count. The
percentage of myeloblasts among the nonerythroid cells ranged from
22.6% to 28.4%. None contained more than 30% pronormoblasts, a
finding that previously has been shown to be a negative prognostic indicator.3,4 None contained sufficient dysplasia to be
classified as acute leukemia with multilineage dysplasia, a diagnosis
that requires dysplasia in at least 50% of the cells of at least 2 lineages.2 In addition, the one case with more than 80%
erythroid precursors revealed erythroid maturation and did not meet the criteria for pure erythroid leukemia.2 All 5 cases were
diagnosed as acute erythroleukemia.
The transition from the French-American-British (FAB) classification of myeloid neoplasms to the WHO classification included a reduction from 30% to 20% in the required blast percentage within the marrow for a diagnosis of acute leukemia, based upon cohort data indicating similar therapeutic responses and outcomes using these 2 thresholds. To our knowledge, there are no analogous data specifically supporting the changes made to diagnostic criteria for acute erythroleukemia. The difference between 30% and 20% myeloblasts as a percentage of NECs in an erythroid-predominant myeloid neoplasm may not represent a true biologic difference but will certainly be used by clinicians making treatment decisions. When the 20% blast percentage cut-off is incorporated into the criteria for erythroleukemia described above, the diagnosis of acute leukemia can be rendered with a relatively low myeloblast percentage. In our cases, the most extreme example was 4% myeloblasts within the bone marrow. In addition, the prevalence of erythroid hyperplasia within cases of myelodysplasia5,6 may make this scenario more commonplace than is currently recognized, since erythroid-predominant cases will require at most 10% total myeloblasts to fulfill criteria for acute erythroleukemia. A patient with 49% erythroid precursors and 10% myeloblasts would be diagnosed as having refractory anemia with excess blasts, type 2 (RAEB-2); the same patient easily could be diagnosed with acute erythroleukemia if the erythroid precursor percentage were determined to be 51% with the same myeloblast percentage. In some cases, other causes of erythroid hyperplasia with slightly elevated blast counts also could be diagnosed incorrectly as acute erythroleukemia. In the absence of data supporting the changes included in the WHO classification, we should critically assess the appropriateness of assigning acute leukemia diagnoses to patients with fewer than 10% (and in one of our cases, fewer than 5%) myeloblasts. These cases of acute erythroleukemia with a low percentage of myeloblasts deserve further study to help determine if there are other relevant clinical, morphologic, and cytogenetic discriminators.
Dale M. Selby, Riccardo Valdez, Bertram Schnitzer, Charles W. Ross, and William G. Finn
References
1.
Vardiman JW, Harris NL, Brunning RD.
The World Health Organization (WHO) classification of the myeloid neoplasms.
Blood.
2002;100:2292-2302 2. Jaffe ES,Harris NL,Stein H,Vardiman JW, eds. World Health Organization Classification of Tumours: Pathology and Genetics of Tumours of Haematopoietic and Lymphoid Tissues. Lyon, France: IARC Press; 2001. 3. Kowal-Vern A, Cotelingham J, Schumacher HR. The prognostic significance of proerythroblasts in acute erythroleukemia. Am J Clin Path. 1992;98:34-40[Medline] [Order article via Infotrieve]. 4. Mazzella FM, Kowal-Vern A, Shrit MA, Wibowo AL, et al. Acute erythroleukemia evaluation of 48 cases with reference to classification, cell proliferation, cytogenetics, and prognosis. Am J Clin Path. 1998;110:590-598[Medline] [Order article via Infotrieve]. 5. Foucar K. Bone Marrow Pathology. Chicago, IL: ASCP Press; 2001. 6. McKenna RW, Allison PM. Diagnosis, classification, and course of myelodysplastic syndromes. Clin Lab Med. 1990;10:683-706[Medline] [Order article via Infotrieve].   CiteULike  Connotea  Del.icio.us  Digg  Reddit  Technorati What's this?
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