Tumor cell lysis syndrome resulting from transient abnormal myelopoiesis in a neonate with Down’s syndrome

transient proliferation of blasts, designated as transient abnormal myelopoiesis (TAM)1 or transient myeloproliferative disorder. The blasts have monoclonality and a megakaryocyte nature with the capacity to differentiate towards multilineage blood cells.2 The disorder is assumed to be different from ‘true malignancy’, because the disease regresses spontaneously. However several complications, including hyperviscosity syndrome, hemorrhage and liver fibrosis, have been described and the prognosis is not always favorable.3–5 Acute tumor cell lysis syndrome (ATLS) is a metabolic disorder characterized by hyperkalemia, hyperuricemia and hyperphosphatemia, which results from rapid degradation of malignant cells after initiation of effective chemotherapy.6 In the present study, we report on a case with TAM, who developed ATLS without any cytotoxic therapies.