“Leukemic” pattern of in vitro growth in a patient with Down syndrome and transient myeloproliferative disorder

Peripheral blood cells from a female infant with Down syndrome and over 60% circulating myeloblasts were cultured in soft agar. Growth was virtually restricted to cluster formation, and cluster-forming cells resided almost exclusively in the very light density fraction (SG < 1.062). Morphological assessment of clusters revealed no evidence of cellular differentiation beyond the blast cell stage. Despite receiving no specific chemotherapy, the peripheral blood normalized within 2 months, and there was no evidence of leukemia when the patient died aged 1 year from cardiac pathology. The findings indicate that caution should be exercised when assessing prognosis on the basis of in vitro growth characteristics in such patients.