B-Lymphoblastic Leukemia in Patients With Chronic Lymphocytic Leukemia

Objectives: B-lymphoblastic leukemia (B-LBL) arising in patients with chronic lymphocytic leukemia (CLL) is exceedingly rare and poorly characterized. Methods: We describe four patients with CLL and concurrent or subsequent B-LBL diagnosed by morphologic, immunophenotypic, cytogenetic, and molecular analysis and reviewed the literature. Results: In three patients, B-LBL followed CLL by 5 to 15 years, and in one patient, B-LBL was diagnosed simultaneously with CLL. In all cases, the CLL had a typical immunophenotype, and the B-LBL blasts showed an immature B-cell immunophenotype with expression of CD10, CD19, and TdT and absence of surface immunoglobulin. In two patients, B-LBL blasts harbored t(9; 22)(q34; q11.2)/BCR-ABL1. We sequenced the IGHV genes in both CLL and B-LBL in two patients and showed that IGHV usage differed. Conclusions: Our data suggest that at least some cases of B-LBL arising in patients with CLL are independent, secondary neoplasms rather than a manifestation of histologic transformation.