MYELODYSPLASTIC SYNDROME IN CHILDREN - DIFFERENTIATION FROM ACUTE MYELOID-LEUKEMIA WITH A LOW BLAST COUNT

To evaluate diagnostic criteria, disease characteristics, and the clin ical course of pediatric myelodysplastic syndrome (MDS), we reviewed 3 27 consecutive cases diagnosed with de novo acute myeloid leukemia (AM L) or MDS at St jude Children's Research Hospital between February 198 0 and January 1993, Among 49 cases with <30% marrow blasts (consistent with FAB criteria and common diagnostic practice for MDS), eight had karyotypes associated with de novo AML (four with t(8;21)(q22;q22) and one each with inv(16)(p13q22), t(11;17)(q23;q21), t(9;11)(p22;q13), a nd i(1)(q10)), We termed these cases AML with a low blast count (AML-L BC) and compared their clinical and morphologic features with those of the remaining 41 cases, AML-LBC cases had little or no hematopoietic dysplasia, MDS cases consisted of refractory anemia (RA, n = 6), RA wi th ring sideroblasts (n = 2), RA with excess blasts (RAEB, n = 4), RAE B in transformation (n = 14), and chronic myelomonocytic leukemia (n = 15), Most had moderate/severe or multilineage hematopoietic dysplasia , with significantly higher dysplasia scores than AML-LBC cases (P = 0 .007), Only 30% of patients with MDS achieved complete remission (CR) after two cycles of AML-directed therapy, compared with 88% of patient s with AML-LBC (P = 0.0001); MDS patients tended to experience prolong ed severe cytopenias with chemotherapy, The Li-year survival for MDS p atients was 23% +/- 7% (s.e.), vs 50% +/- 18% (s.e.) for AML-LBC (P = 0.048), AML-LBC patients frequently had chloromas; none were seen in M DS patients. We conclude that the 30% blast threshold is ineffective f or separation of AML and MDS in pediatric patients, and that genetic d ata should be included in this decision process, AML-LBC, defined by < 30% blasts in bone marrow and cyto- (or molecular) genetic abnormaliti es associated with de novo AML, and characterized by absent or mild ma rrow dysplasia, is biologically and clinically distinct from MDS and s hould he treated as de novo AML. Outcome in pediatric MDS remains poor , and new treatment strategies are needed for these patients.