HYBRID ACUTE LEUKAEMIA

Leukemic blasts with markers of four cell lineages in Down's syndrome ("megakaryoblastic leukemia")

Among 16 patients with Down's syndrome (DS) and acute leukemia admitted to our department during a ten year period, 6 were diagnosed as acute megakaryoblastic leukemia (AMkL). The diagnosis was based on clinical and hematologic criteria, confirmed in three patients with the use of monoclonal antibodies (MoAb) specific for megakaryocytic antigens. In these three, and in a fourth patient, the leukemic blasts were positive for other myeloid, lymphoid and erythroid markers in MoAb testing. We suggest that AMkL in DS is a mixed lineage leukemia with blasts presenting a variety of cell surface antigens, indicating origin from an early progenitor cell with the capability of megakaryocytic differentiation. Of the 6 patients with AMkL, 4 treated with standard AML protocols are in complete continuing remission (CCR) with observation periods from 57+ to 148+ months.

Immunophenotypic and age patterns of childhood acute lymphoblastic leukemia in Saudi Arabia

Acute lymphoblastic leukemia (ALL) is the most common malignancy of childhood in the West, characteristically showing a peak incidence in children aged between two and five years, and being predominantly of the common ALL (cALL) phenotype. In this article, we examine the hypotheses that ALL is relatively less common among childhood malignancies in Saudi Arabia; that the cALL phenotype is uncommon; that T cell ALL (TALL) is relatively more common. We report that of 163 children with ALL seen at the King Faisal Specialist Hospital and Research Centre, we find that their median age was 5.0 years with a modal value of 3 years, with a range of 4 months to 14 years; that there were 93 cALL patients who were predominantly young (median age 5.0 years). There were 20 (12.3%) patients with TALL, whose median age was 8.5 years, 35 (21.5%) patients who were null cell ALL and whose median age was 6.0 years, 14 (8.6%) patients with B cell ALL whose median age was 9.0 years, and 3 (1.8%) patients with mixed phenotype ALL. We also identify a group of 6 (3.7%) patients whose blasts were CD10 negative and showed B cell differentiation without surface membrane immunoglobulin. We conclude that age and phenotypic characteristics of ALL patients are mainly similar to ALL in the West but that L3 was much more common. A small group of six patients showed unusual B cell phenotype and require further evaluation and analysis.