Myelodysplastic and myeloproliferative disorders are rare in childhood and there is no widely accepted system for their diagnosis and classification. We propose minimal diagnostic criteria and a simple classification scheme which, while based on accepted morphological features and conforming with the recent suggestions of the WHO, allows for the special problems of myelodysplastic diseases in children. The classification recognizes three major diagnostic groups:(1) juvenile myelomonocytic leukemia (JMML), previously named chronic myelomonocytic leukemia (CMML) or juvenile chronic myeloid leukemia (JCML);(2) myeloid leukemia of Down syndrome, a disease with distinct clinical and biological features, encompassing both MDS and AML occurring in Down syndrome; and (3) MDS occurring both de novo and as a complication of previous therapy or pre-existing bone marrow disorder (secondary MDS). The main subtypes of MDS are refractory cytopenia (RC) and refractory anemia with excess of blasts (RAEB). It is suggested retaining the subtype of RAEB-T with 20–30% blasts in the marrow until more data are available. Cytogenetics and serial assessments of the patients are essential adjuncts to morphology both in diagnosis and classification.

Background

Myelodysplastic syndrome (MDS) in children and adolescents has hitherto received sparse attention in the pediatric literature and, despite recent attempts, 1, 2, 3, 4, 5, 6 there has been no generally agreed system of classification or diagnosis. Recommendations for the classification of childhood cancer do not even mention MDS. 7 The lack of a generally accepted classification may have contributed to underdiagnosis of MDS in childhood. However, both MDS and juvenile myelomonocytic leukemia (JMML) are uncommon in children, each constituting less than 5% of all hematological malignancies (Table 1).