Impact of pretransplant minimal residual disease on the post‐transplant outcome of pediatric acute lymphoblastic leukemia

There are few reports on the clinical significance of MRD before HSCT in pediatric ALL. We retrospectively analyzed the clinical significance of FCM‐based detection of MRD (FCM‐MRD) before allogeneic HSCT in pediatric ALL. Of 38 pediatric patients who underwent allogeneic HSCT for the first time between 1998 and 2014, 33 patients were in CR and five patients were in non‐CR. The CR group was further divided into two groups based on the pretransplant FCM‐MRD level: the MRD^neg (<0.01%; 30 patients) group and the MRD^pos (≥0.01%; three patients) group. There were significant differences in the three‐yr event‐free survival rates between the CR and non‐CR group, and between the MRD^neg and MRD^pos group. The three‐yr cumulative RI in the MRD^neg group were 27.3% ± 8.8%, whereas two of the three patients in the MRD^pos group relapsed within one yr after HSCT. The clinical outcome of the MRD^pos group was as poor as that of the non‐CR group in pediatric ALL. Therefore, an improvement in pretransplant treatment that aims to achieve a more profound remission would contribute to reducing the risk of relapse.