In summary, the history of hematology/oncology in Canada is a varied one. Beginning in 1945 in hematology, it has gradually expanded to include oncology. The growth of this specialty has provided a high standard of medical care and free services to afflicted children and their families. A substantial amount of basic and clinical research is carried out in this field. A great deal of work remains to be done in Canada, as elsewhere, if the needs of all patients are to be met and the diseases afflicting them are to be adequately studied.
The incidence of leukemia is higher in children with Down syndrome (DS) than in normals. In approximately 50% of cases the type of leukemia is acute megakaryoblastic leukemia (AMKL) and it occurs during the first 4 years of life. The leukemic cell also has features of erythroid progenitors and therefore appears to be a precursor cell with biphenotypic properties. In addition, newborns with DS frequently develop transient leukemia (TL), which is characterized by the presence of megakaryoblasts in the blood which disappear during the first 1-3 months of life. The incidence of this disorder is unknown although preliminary studies suggest that megakaryoblasts may be found frequently in the blood of DS newborns. TL does not occur in normal newborn infants. Although TL disappears spontaneously, many of these children will develop AMKL at 1-4 years of age. Recent surveys suggest that 20-30% of newborns with TL will develop AMKL. Preliminary evidence suggests that TL is a clonal proliferation, can be fatal, and may occur in a specific subgroup of DS children. The observations in this report are drawn from our own experience, reports in the literature, and data accumulated in the Canadian Down Syndrome Leukemia Registry.
Megakaryoblastic leukemia and transient leukemia in Down's syndrome have been reviewed using case reports from the literature and our own experience at the Hospital for Sick Children. The following conclusions have been reached: (1) approximately 20% of leukemia (excluding transient leukemia) in Down's syndrome is acute megakaryoblastic leukemia; (2) approximately 20% of all leukemia in Down's syndrome is transient leukemia; (3) transient leukemia in Down's syndrome is acute megakaryoblastic leukemia; (4) recurrence of acute megakaryoblastic leukemia occurs in 20% of the cases of transient leukemia; and (5) the incidence of acute megakaryoblastic leukemia in Down's syndrome is estimated to be 400 times that in normal children. These observations suggest that a specific form of leukemia, namely acute megakaryoblastic leukemia, has a remarkable association with Down's syndrome.
