Downs syndrome is the most common postnatally viable chromosomal anomaly. Certain malignancies occur more frequently in persons with Downs syndrome compared to others. They include leukaemias, gonadal and extragonadal germ cell tumours and retinoblastomas. Children and adolescents with Downs Syndrome have a 10-30 fold increased incidence of leukaemia. This suggests an important role for some chromosome 21 genes located in leukaemogenesis. 

 

The age of onset for leukaemia in Downs syndrome is bimodal, peaking first in the newborn period and again at 3 to 6 years. Four Congenital leukaemia also occurs with increased frequency in Downs syndrome and is characterized by a preponderance of acute myeloblastic leukaemia as in non-Down syndrome children. Acute myeloblastic leukaemia in Downs syndrome almost exclusively presents before the age of four years and the commonest type is acute megakaryoblastic which is extremely rare in non-Downs syndrome children.