High Predictive Value of Pre Transplant Minimal Residual Disease Assessment By Combining WT1 Expression and Flow Cytometry in Acute Myeloid Leukemia

BACKGROUND AND AIMS Allogeneic bone marrow transplantation (BMT) offers the greatest chance of cure for patients with high-risk acute myeloid leukemia (AML). Persistence of disease or high levels of pre BMT minimal residual disease (MRD) have been reported to predict relapse risk after BMT. WT1 expression levels and multicolor flow cytometry (MFC) are the most common tools to evaluate MRD. We recently reported that combining WT1 expression and MFC for MRD detection after induction therapy strongly impacts on relapse risk in AML. The aim of this study was to analyze the role of pre-BMT MRD assessment as predictor for the post-transplant relapse risk. MATERIALS AND METHODS We retrospectively analyzed the outcome of 253 consecutive AML patients receiving allo-BMT. Pre-BMT marrow samples were analysed for WT1 expression and MFC as MRD evaluation . Median age at transplant was 45 years. Disease phase was CR1 in 161, CR2 in 63, and CR3 in 29 patients. One hundred eighty-two received myeloablative conditioning, whereas 71 patients received reduced intensity conditioning. Median follow-up was 59 months (95% CI 46.2 - 71.8 months). Relapse-free survival (RFS) was calculated from the time of transplantation until last follow-up or documented leukemic relapse. Overall Survival (OS) was calculated from the time of transplantation until death by any cause or last follow-up. A positive MFC MRD was defined by the presence of no less than 25 clustered leukemic cells/10 5 total events (threshold of 2.5x10 -4 residual leukemic cells) at four-color flow-cytometry. Real-time PCR for WT1 was performed on DNA Engine 2 (Opticon®, MJ Research®). WT1 copy number/Abl copy number 500x10 4 was used as cut-off value for abnormal WT1 expression. RESULTS Relapse occurred in 81 patients (32%). Three-year estimate of RFS was 63.7% (median not reached). The probability of relapse was significantly affected by disease status (first or subsequent CR, p Specifically, MFC-MRD was the strongest predictor of longer relapse free survival (p CONCLUSIONS Pre transplant MRD evaluation by WT1 and MFC on bone marrow samples is a reliable predictor of relapse risk. Patients with both negative pre-BMT MRD markers have a significantly longer RFS, while patients with both positive MRD markers display an higher risk of relapse. Identifying patients who have an higher risk of relapse could open the way to apply pre-emptive therapeutic strategies to prevent AML relapse, from donor lymphocyte infusion to other innovative approaches. Disclosures No relevant conflicts of interest to declare.