A case of TdT-positive B-cell acute lymphoblastic leukemia

The phenotypic marker profile of a patient with B-cell acute lymphoblastic leukemia (B-ALL) is described. The blast cells showed typical FAB L3 morphology, had the characteristic t(8;14) chromosomal abnormality, and were monoclonal in the expression of surface immunoglobulins. The clinical course of this patient is consistent with the poor prognosis described for B-ALL cases. Surface marker analysis identified cells positive for surface immunoglobulins, Ia-like antigen, common ALL-antigen, and terminal deoxynucleotidyl transferase. This marker profile shows immunologic characteristics of the two B-cell leukemia subtypes, pre-B-ALL and B-ALL. This "intermediate" immunologic phenotype might either be the result of an uncoupling of the sequential immunologic maturation processes or of an arrest of the cells at an intermediate stage between the two otherwise clearly defined leukemia subtypes, but closer to the typical B-ALL stage. This latter observation is supported by isoenzyme marker analysis, as the cells were negative for the hexosaminidase I isoenzyme, which is positive in pre-B-ALL but negative in B-ALL.