Background and aims Children diagnosed with Down syndrome have a distinctive predisposition to develop acute myeloblastic leukaemia of Down syndrome (ML-DS). This disease is preceded by a transient neonatal preleukemic state known as transient myeloproliferative disorder (TMD) which can be clinically obvious or silent. This condition is considered to be a paradox in oncology because it regresses spontaneously three months after birth, with a 5 year survival rate of approximately 80%.

Methods We report a case of a 3 year old girl with Down syndrome who was monitored in our clinic since she was one month old.

Results The patient was born with a Down phenotype from a dizygotic twin pregnancy, with a healthy brother. At the age of 8 days she started to present pallor and splenomegaly. Leukocytosis and thrombocytopenia were present and the May-Grunwald-Giemsa stained smears revealed 78% blasts, the aspect suggesting an acute congenital leukaemia, probably megakarioblastic. The immunophenotyping confirmed this diagnosis. The patient was diagnosed with TMD and achieved spontaneous complete remission at the age of 8 weeks and was periodically monitored in our department. At the age of 3 years she was admitted to our hospital with bleeding gums, petechiae and splenomegaly. The peripheral blood count revealed 70% blasts, anaemia and thrombocytopenia. The bone marrow aspirate concluded that it was an acute mixed phenotype, myeloid and B-lymphoblastic leukaemia. The patient started therapy with the AML-BFM 2004 protocol, achieving complete remission after the first block of chemotherapy.

ConclutionS It is estimated that 20%–30% of the neonates with TMD will eventually develop ML-DS. The blasts are similar to those in TMD, with a megakarioblastic morphology. However, in our case, the blasts first had the typical morphology, but when the patient developed ML-DS blasts had both myeloblastic and lymphoblastic characteristics. TMD and ML-DS have distinctive features which make it an exceptional in vitro model for myeloid leukemogenesis.