Purpose: A unique myelodysplastic syndrome referred to as transient abnormal myelopoiesis (TAM) has been reported to occur primarily in infants with Down's syndrome (DS) or other abnormalities of chromosome 21. This disorder raises basic questions regarding the pathogenesis of leukemia, yet its natural history is poorly documented and derives from small series and isolated case reports.
Patients and methods: To better characterize TAM, we accumulated data on 35 cases identified through a questionnaire mailed to pediatric oncologists in the United States. These cases, pooled with two that we recently encountered, and 58 comparable cases reported in the literature comprise a series of 95 cases of TAM in DS.
Results: The patients in this series were notable for the high morbidity and mortality of this reportedly benign condition. Eleven percent of the patients died during the initial event, and the overall mortality for the entire series was 27%. Twenty-eight of the 85 patients (33%) who survived the initial event developed a subsequent hematologic disorder, most often acute nonlymphocytic leukemia, at a median age of 16 months.
Conclusions: No initial clinical or hematologic features predicted the development of a subsequent hematologic disorder. However, those patients initially mosaic for the presence of trisomy 21 did not develop subsequent abnormalities. This series reviews questions regarding leukemogenesis in DS and underscores the importance of conducting future prospective studies of this unique hematologic disorder.