Mimics and artefacts of measurable residual disease in a highly sensitive multicolour flow cytometry assay for B-lymphoblastic leukaemia/lymphoma: critical consideration for analysis of measurable residual disease

High-sensitivity multicolour flow cytometry (MFC)-based B-lymphoblastic leukaemia (B-ALL) measurable residual disease (BMRD) assay is increasingly being used in clinical practice. Herein, we describe six consistently present low-level populations immunophenotypically mimicking abnormal B-ALL blasts in 441 BMRD samples from 301 children. These included CD19(+)CD123(+) plasmacytoid dendritic cells differentiating from lymphoid precursors, CD10(+) transitional B cells with CD10(+)/CD38dim-to-negative/CD20bright/CD45bright phenotype, CD19(+) natural killer (NK) cells, CD73bright/CD10(+) mesenchymal stromal/stem cells, CD73bright/CD34(+) endothelial cells, and a CD34(+)CD38dim-to-negative/CD10(-)/CD20bright/CD45bright subset of mature B cells. We provide the proportions, comprehensive immunophenotype, and practical clues for proper identification of these low-level populations. Knowledge regarding the presence and immunophenotype of these mimics is essential for accurate interpretation in high-sensitivity MFC-BMRD analysis.

Automated summary

The study identifies six consistently present low-level populations in 441 BMRD samples from 301 children, which immunophenotypically mimic abnormal B-ALL blasts. Understanding the presence and immunophenotype of these mimics is crucial for accurate interpretation in high-sensitivity MFC-BMRD analysis.