Molecular characteristics of terminal deoxynucleotidyl transferase negative precursor B‐cell phenotype Burkitt leukemia with IGH‐MYC rearrangement

Precursor B cell phenotype Burkitt lymphoma/leukemia with IGH-MYC is a rare subtype of Burkitt lymphoma (BL). BL and B lymphoblastic leukemia/lymphoma (B-ALL/LBL) differ as regards treatment and the distinction between these two entities is crucial. Patients demonstrating a terminal deoxynucleotidyl transferase (TdT)-positive precursor B cell phenotype with IGH-MYC rearrangement have been reported to be molecularly distinct from BL and closer to B-ALL/LBL. We investigated the molecular characteristics of two cases of a rare but distinct TdT-negative precursor B cell phenotype BL. Both patients showed FAB L3 morphology with IGH-MYC translocation, but had precursor B cell immunophenotypes including dim to moderate expression of CD45 and absence of BCL6, CD20, monoclonal kappa, and lambda light chain expression. To characterize the molecular features, we performed exome sequencing and analyzed the breakpoint junction of the IGH-MYC rearrangement. We detected KMT2D mutations in both cases, a rarely acquired chromatin modifying gene mutation in BL. The breakpoint analysis revealed that the IGH-MYC rearrangement occurred due to an aberrant VDJ recombination in one case. The treatment protocols differed, including high-grade lymphoma treatment and standard B-ALL treatment. Complete remission was achieved in the patient who received B-ALL treatment. The degree of resemblance of BL and B-ALL differed between two cases, but the molecular pathogenesis and manifesting features of both TdT-negative precursor B cell phenotype BL case were distinct from classic BL, which indicates the need for a better understanding of this uncommon entity that does not fit in current diagnostic and classification categories.