RUNX1 rearrangement in mature B-cell acute lymphoblastic leukemia with non-L3 morphology

Area of Science:

• Hematology
• Oncology
• Genetics

Background:

• Mature B-cell acute lymphoblastic leukemia (ALL) is typically characterized by surface immunoglobulin (sIg) expression and features of Burkitt lymphoma (FAB-L3 morphology, MYC rearrangement).
• Distinct subtypes of mature B-cell ALL have been identified, including those with non-L3 morphology and KMT2A rearrangement in pediatric cases.

Observation:

• A 65-year-old male presented with leukocytosis and thrombocytopenia.
• Bone marrow examination revealed 97.8% myeloperoxidase-negative blasts with L2 morphology and mature B-cell immunophenotype (sIg-κ+, CD19+, CD20+, CD22+, CD79a+, TdT-, CD34-).
• Cytogenetic analysis identified a complex karyotype including inv(21)(p13q22.1) with RUNX1 rearrangement, while MYC and KMT2A rearrangements were absent.

Findings:

• This is the first reported case of mature B-cell ALL presenting with RUNX1 rearrangement.
• The identified inv(21)(p13q22.1) involving RUNX1 represents a novel cytogenetic aberration in this context.

Implications:

• The findings suggest that RUNX1 rearrangement may be implicated in the pathogenesis of mature B-cell ALL, particularly in cases with non-L3 morphology and without MYC rearrangement.
• This discovery expands the known genetic landscape of mature B-cell ALL and may inform future diagnostic and therapeutic strategies.