Droplet Digital PCR Outperforms Conventional Methods for Early Relapse Prediction in Acute Myeloid Leukemia/Myelodysplastic Syndrome Patients Post-Transplantation

Relapse remains a major challenge after allogeneic hematopoietic stem cell transplantation (allo-HSCT) for myeloid malignancies. Early detection of relapse is critical for timely intervention, and measurable residual disease (MRD) and donor chimerism (DC) monitoring are key strategies for relapse prediction. While conventional methods such as quantitative PCR for Wilms' tumor 1 mRNA levels (WT1-qPCR), multiparameter flow cytometry (MFC), short tandem repeat (STR) chimerism, and fluorescence in situ hybridization for the X and Y chromosomes (XY-FISH) are widely used, their sensitivity and specificity vary. Droplet digital PCR (ddPCR), a highly sensitive quantitative technique, offers potential advantages in mutation detection and MRD tracking, but its comparative efficacy in predicting relapse with conventional methods post-transplantation remains to be fully established. This study aimed to evaluate the performance of ddPCR in predicting relapse after allo-HSCT compared to conventional MRD and chimerism monitoring methods (WT1-qPCR, MFC, STR, and XY-FISH). The study included 196 patients with myeloid malignancies who underwent allo-HSCT. MRD and DC were monitored using ddPCR, WT1-qPCR, MFC, STR (total-DC and T-DC), and XY-FISH. The sensitivity, specificity, false-negative rate, false-positive rate, and Youden index were calculated to assess their predictive efficacy. The lead time for relapse prediction (median days before clinical relapse) was also compared across techniques. ddPCR demonstrated superior sensitivity (81.08%) and specificity (91.19%) compared with WT1-qPCR (75.86%/78.23%) and MFC (56.76%/94.97%). The sensitivities and specificities of total-DC (16.13%/94.70%), T-DC (9.68%/93.94%), and XY-FISH (46.67%/79.73%) were significantly lower. From the most robust to inconclusive, the efficacies of the techniques in predicting relapse (Youden index) were as follows: 0.72 for ddPCR, 0.54 for WT1-qPCR, 0.51 for MFC, 0.26 for XY-FISH, 0.11 for total-DC, and 0.04 for T-DC. Notably, ddPCR provided the earliest relapse prediction, with a median lead time of 60.5 (range: 10 to 461) days, outperforming MFC (43 days), WT1-qPCR (55 days), STR chimerism (total-DC: 43 days; T-DC: 37 days), and XY-FISH (54 days). This study suggests that ddPCR may be a transformative tool for MRD monitoring with the superior sensitivity and longer lead time for predicting relapse than conventional methods in acute myeloid leukemia/myelodysplastic syndrome patients after allo-HSCT. Its outstanding performance supports its integration into routine post-transplant monitoring to enable early intervention and improve outcomes.