Transitional pre-B-cell acute lymphoblastic leukemia of childhood is associated with favorable prognostic clinical features and an excellent outcome: A pediatric oncology group study

The presenting characteristics and survival of children with the newly recognized transitional cell pre-B imrnunophenotype of acute lymphoblastic leukemia (ALL) are compared with those of children with pre-B ALL to determine the clinical significance of the new phenotype. Patients with transitional pre-B ALL (n = 17), defined by lymphoblasts expressing cytoplasmic and surface μ heavy chains without κ or λ light chains, have lower initial leukocyte counts (p = 0.02) and a higher frequency of DNA indexes > 1.16 (p < 0.001) than patients with pre-B ALL (n = 501), whether or not cases with the unfavorable prognostic (1;19) translocation are included in the analysis. Patients with transitional pre-B ALL lack FAB L3 morphology, bulky extramedullary disease, surface κ or λ chains, and the (8;14), (8;22), and (2;8) translocations, features that characterize the syndrome of B-cell ALL. The 4-year relapse-free survival result for children with transitional pre-B ALL appears better than that for children with pre-B ALL (93.3 ± 17% versus 72.9% ± 4.6%), but this difference is not statistically significant. We conclude that patients with transitional pre-B ALL have a very favorable prognosis in the context of the therapy used in this study.