CD33+ B-cell precursor acute lymphoblastic leukemia in children: a distinct subgroup of B-cell precursor acute lymphoblastic leukemia.

Clinical and laboratory features associated with CD33 expression were analysed in 123 children with B-precursor acute lymphoblastic leukemia (ALL), including 85 at onset, 34 at relapse and four in a refractory state to induction therapy. CD33 was demonstrated in 13 patients (15.3%) at onset, and it was associated with coexpression of T-cell and multipotential hematopoietic cell-associated antigens, i.e. CD2, CD4 and CD7, which were observed in four of 11 analysed patients (P < 0.01). Patients with CD33 expression were older than those without CD33 (P < 0.01). Although CD33 was the strongest predictor of a poor outcome (event-free survival, 44% for CD33+ and 75% for CD33-patients; P = 0.0041) in univariate analysis, multivariate analysis did not demonstrate significance (P = 0.0645). Fourteen of 38 patients (36.8%) at relapse or in a refractory state showed CD33 expression. Analysis of CD33 expression had also been performed at onset in 16 of these patients and showed acquisition of CD33 in six of 13 patients who had been negative for this antigen at onset. Thus, it seems that CD33+ B-precursor ALL is derived from undifferentiated cells minimally committed to B-cell lineage and more homogeneous than so-called My+ B-precursor ALL with regard to the clinical and biological features. The frequent expression of CD33 on the cells which acquired resistance to chemotherapy may have resulted from expansion of a CD33+ original minor clone or clonal evolution.