Phenotypic and karyotypic properties of hyperdiploid acute lymphoblastic leukaemia of childhood

The DNA/cell content was measured by flow cytometry in samples obtained from 98 unselected children with acute lymphocytic leukaemia (ALL) at diagnosis. The frequency of anomalies in modal DNA content was compared to that encountered in acute childhood non-lymphocytic leukaemia (ANLL) and disseminated non-Hodgkin's lymphoma (NHL). In ALL the most frequent (35%) aberration in DNA content was an increase by 20% relative to the modal value of normal white blood cells. This subcategory, referred to as hyperdiploid ALL (HD-ALL), was characterized by a close association with the expression of the c-ALL surface marker (20/20 patients) and characteristic numerical chromosome changes, including tri- or tetrasomy of chromosome 21. Moreover, patients with hyperdiploid ALL had a much lower peripheral leucocyte count (P = 0.001) than those with diploid disease and a varying proportion of their leukaemic cells existed in the peripheral blood as morphologically normal lymphocytes expressing the c-ALL antigen. Within the standard risk category, patients with HD-ALL had a longer disease-free survival than those with diploid disease (P = 0.058). It is concluded that routine analysis by flow cytometry can conveniently and consistently detect ALL patients with hyperdiploid chromosome numbers. Hyperdiploid ALL constitutes a fairly large subtype of childhood ALL with specific biological and karyotypic properties, possibly associated with favourable prognosis.