Summary: Allogeneic haematopoietic stem cell transplantation (HSCT) is still considered to play an important role as a consolidation therapy for high-risk infants with acute lymphoblastic leukaemia (ALL). Here, we retrospectively analysed outcomes of HSCT in infants with ALL based on nationwide registry data of the Japan Society for Haematopoietic Cell Transplantation. A total of 132 allogeneic HSCT for infant ALL with KMT2A (MLL) gene rearrangements, which were performed in first complete remission (CR1), were analysed. The 5-year overall survival rate after transplantation was 67·4 ± 4·5%). Although recent HSCT (after 2004) had a trend toward better survival, no statistical correlation was observed between outcomes and each factor, including age at diagnosis, initial leucocyte count, cytogenetics, donor types or conditioning of HSCT. Myeloablative conditioning with total body irradiation did not provide a better survival (60·7 ± 9·2%) over that with busulfan (BU; 67·8 ± 5·7%). Two of the 28 patients treated with irradiation, but none of the 90 BU-treated patients, developed a secondary malignant neoplasm. In conclusion, allogeneic HSCT using BU was a valuable option for infant ALL with KMT2A rearrangements in CR1.
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