Transient leukemia in newborns without down syndrome: diagnostic and management challenges.

Transient leukemia (TL), defined by circulating nonlymphoid blast in the peripheral blood, occurs in approximately 10% of infants with constitutional trisomy 21 (Down syndrome). The TL phenotype may also occur in newborns who do not have clinical signs of Down syndrome but nonconstitutional trisomy 21 due to mosaicism. We report the cases of 3 infants to highlight the specific parental concerns, diagnostic and counseling requirements for this group of infants and their families and suggest a practical approach to diagnosis, follow-up, anticipatory guidance, and discussion of prognosis for families with newborns diagnosed with TL and nonconstitutional trisomy 21.