Letters to the Editor 1321 pluripotent stem cell. However, the fact that not all CD34- Bobigny, France; 5 positive or all BFU-E or CFU-GM colonies are positive for Third Department of Internal Medicine, Semmelweis University, Budapest, Hungary; V617F suggests that the bone marrow of this patient is not 6 monoclonal with respect to the JAK2 mutation. Department of Haematology, University Hospital Linko¨ping, Linko¨ping, Sweden; In summary, the JAK2 V617F mutation was detected in a 7Genomics center, School of Biomedical and Health Sciences, cohort of patients with 5qÀ syndrome and a hypercellular Kings College London, London, UK; marrow. Despite no statistical difference, a higher median 8National Health Centre, Semmelweis University, platelet count was observed in the mutant cases with 50% (3/6) Budapest, Hungary; showing a platelet count 4700 Â 109/l compared with only 3% 9Institute of Pathology and Cancer Research, Semmelweis (3/91) in the wild-type cases. The lack of clinical response to University, Budapest, Hungary and 10 erythropoietin in the two cases described fails to support Department of Oncology and Clinical Immunology, previous in vitro studies documenting hypersensitivity to St-Johannes-Hospital, Duisburg, Germany erythropoietin in the presence of the mutation. E-mail: [email protected] 11These authors contributed equally to this work Whether the JAK2 mutation occurs as an early or late event during the disease course is unclear. We detected the JAK2 mutation both at time of diagnosis and at a follow-up of 132 References months in one case analysed, suggesting that the mutation occurred as an early event. Longer follow-up is however 1 James C, Ugo V, Le Couedic JP, Staerk J, Delhommeau F, Lacout C necessary to determine the prognostic significance of JAK2 et al. A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera. Nature 2005; 434: 1144– mutation and in particular, whether these cases will show 1148. favourable response to lenalidomide as previously demonstrated 2 Levine RL, Wadleigh M, Cools J, Ebert BL, Wernig G, Huntly BJ in 5qÀ chromosomal abnormalities.8 et al. Activating mutation in the tyrosine kinase JAK2 in polycythemia vera, essential thrombocythemia, and myeloid metaplasia with myelofibrosis. Cancer Cell 2005; 7: 387–397. Acknowledgements 3 Kralovics R, Passamonti F, Buser AS, Teo SS, Tiedt R, Passweg JR et al. A gain-of-function mutation of JAK2 in myeloproliferative W Ingram is supported by the Leukaemia Research Fund, UK. disorders. N Engl J Med 2005; 352: 1779–1790. 4 Baxter EJ, Scott LM, Campbell PJ, East C, Fourouclas N, Swanton S et al. Acquired mutation of the tyrosine kinase JAK2 in human W Ingram1,11, NC Lea1,11, J Cervera2, U Germing3, P Fenaux4, myeloproliferative disorders. Lancet 2005; 365: 1054–1061. B Cassinat4, JJ Kiladjian4, J Varkonyi5, P Antunovic6, 5 Steensma DP, Dewald GW, Lasho TL, Powell HL, McClure RF, NB Westwood1, MJ Arno7, A Mohamedali1, J Gaken1, Levine RL et al. The JAK2 V617F activating tyrosine kinase T Kontou1, BH Czepulkowski1, NA Twine1, J Tamaska8, mutation is an infrequent event in both ‘atypical’ myeloprolife- J Csomer9, S Benedek5, N Gattermann3, E Zipperer3, rative disorders and myelodysplastic syndromes. Blood 2005; 106: 1207–1209. A Giagounidis10, Z Garcia-Casado2, G Sanz2 and GJ Mufti1 1 6 Jones AV, Kreil S, Zoi K, Waghorn K, Curtis C, Zhang L et al. Department of Haematological Medicine, Kings College Widespread occurrence of the JAK2 V617F mutation in chronic Hospital and Kings College London, London, UK; 2 myeloproliferative disorders. Blood 2005; 106: 2162–2168. The Servicio de Hematologia y Hemoterapia, Hospital 7 James C, Delhommeau F, Marzac C, Teyssandier I, Couedic JP, Universitario La Fe, Valencia, Spain; 3 Giraudier S et al. Detection of JAK2 V617F as a first intention Department of Haematology, Oncology and Clinical diagnostic test for erythrocytosis. Leukemia 2006; 20: 350–353. Immunology, Heinrich-Heine-University, 8 List A, Kurtin S, Roe DJ, Buresh A, Mahadevan D, Fuchs D et al. Du¨sseldorf, Germany; Efficacy of lenalidomide in myelodysplastic syndromes. N Engl J 4Hematology Department at Hopital Avicenne, Med 2005; 352: 549–557. Immunophenotypic identification of acute myeloid leukemia with monocytic differentiation Leukemia (2006) 20, 1321–1324. doi:10.1038/sj.leu.2404242; biologic diversity within FAB AML subtypes led to the World published online 27 April 2006 Health Organization (WHO) classification of AML, published in 2001, in which morphologic, immunophenotypic, genetic, and clinical features of AML were included in defining disease In 1976, the French-American-British (FAB) Cooperative entities.3 By WHO criteria, cases previously diagnosed as FAB Group published a morphologic classification of acute myeloid M4 or M5 may be classified as AML with recurrent cytogenetic leukemia (AML).1 A revision of this classification published in abnormalities (inv(16)(p13q22)/t(16;16)(p13;q22)(CBFb/MYH11), 1985 was widely used and recognized as the standard for AML 11q23(MLL), or t(8;21)(q22;q22)(AML1/ETO)), AML with multi- classification for over 15 years.2 Included in the FAB classifica- lineage dysplasia, therapy related AML, and AMML or AMoL tion were two groups of AML that exhibited monocytic subtypes of AML not otherwise categorized (NOC). Appropriate differentiation, acute myelomonocytic leukemia (AMML; M4), classification of AML is important for clinical management and and acute monoblastic/monocytic leukemia (AMoL; M5). A allows for future studies to expand and refine our understanding subset of M4 with abnormal and increased eosinophils (M4EO) of these diseases. was found to be associated with chromosome 16 abnormalities, While immunophenotypic features are included in the WHO either inv(16)(p13q22) or t(16;16)(p13;q22). Recognition of the classification of AML, immunophenotypic criteria for monocytic Leukemia Letters to the Editor 1322 54 Figure 1 Frequency of antigen expression in blasts of acute HLA-DR 100 monoblastic/monocytic leukemia (AMoL) (n ¼ 23) and nonmonocytic 60 leukemia (NM-AML) (n ¼ 72). Solid bars: AMoL; open bars: CD64 100 NM ¼ AML. 26 CD56 85 17 AML have not been clearly defined. A high level of expression of CD36 06 CD14 is a specific feature of mature monocytes, but this antigen 68 CD34 is frequently absent or underexpressed on immature monocytic 17 cells. Furthermore, other antigens that are generally considered 94 to be monocyte-associated may be expressed in other types of CD33 100 AML. The goals of the present study were to identify 0 immunophenotypic patterns that reliably characterize mono- Antigens CD16 38 cytic AMLs and to explore their immunophenotypic 74 heterogeneity in relationship to morphologic and cytogenetic CD15 100 subgroups. 0 A total of 126 cases of de novo AML diagnosed and analyzed CD14 61 with 4-color flow cytometry at our institution from 1998 to 2004 100 were included in the study. All cases were classified according CD13 83 to FAB criteria2 based on morphology and cytochemical 33 reactivity for myeloperoxidase and alpha naphthyl butyrate CD11b 100 esterase (ANBE), and also according to WHO criteria3 based on 30 clinical, morphologic, immunophenotypic, and cytogenetic CD4 100 features. By FAB criteria, 54 exhibited morphologic and cytochemical features of monocytic AML, including 31 cases 020406080 100 120 of M4 and 23 cases of M5 (15 monoblastic and eight Antigen Expression in % monocytic). Those 54 cases were classified by WHO criteria Figure 2 Expression patterns of CD36 in blasts of acute myeloid leukemia (AML) with monocytic differentiation. (a) Blasts (red) in acute monoblastic leukemia coexpressed CD36 and CD64. (b) Group 1 acute myelomonocytic leukemia (AMML) with one population (red) in the blast/ monocytic region, which showed a spectrum of CD36 and CD64. The least differentiated blasts were CD36(À) and CD45(moderate), followed by acquisition of CD36, and finally progression to bright CD45 expression. (c) Group 2 AMML with distinct population of blasts (red) and monocytes (blue) in the CD5/SSC dot plot. Both populations formed distinct clusters in the expression of CD36 and CD64. Green: granulocytes. Leukemia Letters to the Editor 1323 as AML with t(8;21) (3), inv(16)/t(16;16) (7), or 11q23 (11); However, all AMoLs in our series were positive for CD11b AML with multilineage dysplasia (3); or AML NOC (30). Of and HLA-DR, while none of the APLs expressed both antigens the 30 AML NOC cases, 17 were classified as AMML and 13 (data not shown). Furthermore, intense myeloperoxidase ex- as AMoL. pression, either by cytochemistry or flow cytometry, should help By flow cytometric analysis, blasts and monocytes were to distinguish microgranular APL from AMoL. identified using CD45/side scatter (SSC)/forward scatter (FSC) Cases of FAB M4 AML could be divided into two groups characteristics in combination with various cell surface anti- based on the definitive separation of discrete subpopulation of gens. The frequency of antigen expression in 23 AMoLs was blasts and monocytic cells in the analysis of CD45 and light compared to 72 nonmonocytic AMLs (NM-AML) (Figure 1). scatter (Figure 2b and c). One group showed a single Overall, the blasts in AMoL more frequently expressed CD4, (indistinguishable) population composed of both blasts and CD11b, CD14, CD16, CD36, CD56, CD64, and HLA-DR, and monocytic cells (designated group 1; 11 cases) (Figure 2b). The less often expressed CD34 compared to NM-AMLs (each immature cells in all cases of group 1 coexpressed CD36 and Po0.01). As single markers, none of these were sufficiently CD64. Thus, immunophenotypically, these closely resembled sensitive and specific for identifying monocytic AML. CD14 the AMoLs in our series, but were distinguished by a substantial expression in the blast/immature monocytic population was population of maturing granulocytes. Although discrete popula- seen in all eight cases of acute monocytic leukemia, but in eight tion of blasts and monocytic cells could not be discriminated in of 15 cases of acute monoblastic leukemia (P ¼ 0.021).