KMT2A and acute lymphoblastic leukemia: We conducted long-term follow-up of 124 children with ALL included in this study, and eventually 5 children relapsed, with a significantly higher proportion of MLL-r positive children relapsing than in the negative group, and all of them relapsed in bone marrow alone and had high-risk factors for poor prognosis such as WBC ≥ 50 × 109/L, T-cell phenotype or positive D15 MRD, consistent with the literature [10–15].