Comparative analysis of BCR::ABL1 p210 mRNA transcript quantification and ratio to ABL1 control gene converted to the International Scale by chip digital PCR and droplet digital PCR for monitoring patients with chronic myeloid leukemia

Objectives: Chronic myeloid leukemia (CML) is characterized by the Philadelphia chromosome, leading to the BCR::ABL1 fusion gene and hyper-proliferation of granulocytes. Tyrosine kinase inhibitors (TKIs) are effective, and minimal residual disease (MRD) monitoring is crucial. Digital PCR platforms offer increased precision compared to quantitative PCR but lack comparative studies. Methods: Eighty CML patient samples were analyzed in parallel using digital droplet PCR (ddPCR) (QXDx™ BCR-ABL %IS Kit) and chip digital PCR (cdPCR) (Dr. PCR™ BCR-ABL1 Major IS Detection Kit). Results: Overall, qualitative and quantitative agreement was good. Sensitivity analysis showed positive percentage agreement and negative percentage agreement were both ≥90%, and the quadratic weighted kappa index for molecular response (MR) level categorization was 0.94 (95%CI 0.89, 0.98). MR levels subgroup analysis showed perfect categorical agreement on MR level at MR3 or above, while 35.4% (17/48) of patient samples with MR4 or below showed discordant categorizations. Overall, Lin's concordance correlation coefficient (CCC) for the ratio of %BCR::ABL1/ABL1 converted to the International Scale (BCR::ABL1^IS) was almost perfect quantitative agreement (Lin's CCC=0.99). By subgroups of MR levels, Lin's CCC showed a quantitative agreement of BCR::ABL1^IS decreased as MR deepened. Conclusions: Both cdPCR and ddPCR demonstrated comparable performance in detecting BCR::ABL1 transcripts with high concordance in MR3 level or above. Choosing between platforms may depend on cost, workflow, and sensitivity requirements.