Haploidentical Hematopoietic Stem Cell Transplantation May Improve Prognosis in Non-Infant Children with t(v;11q23)/MLL-Rearranged B-Acute Lymphoblastic Leukemia

Background: B-acute lymphoblastic leukemia (B-ALL) with t(v;11q23)/MLL-rearrangement (MLL-r) in children (1 year or older) is rare, and its outcome and optimal treatment options remain controversial. This study aimed to analyze the clinical characteristics and outcomes of these patients, and to explore the role of allogeneic hematopoietic stem cell transplantation (allo-HSCT), especially haploidentical HSCT (haplo-HSCT) in the treatment of these patients.

Methods: At the time of the last follow-up (July 1, 2019), we retrospectively analyzed clinical data of 42 non-infant children with t(v;11q23)/MLL-r B-ALL. Comparison of outcomes was made between patients received allo-HSCT in the first complete remission (CR1) and chemotherapy only.

Results: The median follow-up was 41 (1-106) months. The median age at diagnosis was 4.5(1-14) years and the median leukocyte count was 56.0 (2.2-735.2)×10⁹/L. One was excluded for death during induction. For the remaining 41 patients, the complete remission rate after induction therapy was 40/41 (97.6%), the estimated 4-year probabilities of overall survival (OS), event-free survival (EFS) and cumulative incidence of relapse (CIR) were 59.7%, 51.6% and 43.4%, respectively. 19 patients received allo-HSCT in CR1 (HSCT in CR1 cohort), notably, 18/19 cases in this cohort received haplo-HSCT, and the remaining 22 patients continued the consolidation therapy (Non-HSCT in CR1 cohort). The estimated 4-year probabilities of OS, EFS and CIR in the HSCT in CR1 cohort were 86.6%, 89.2% and 5.3%, respectively. Meanwhile, the estimated 4-year probabilities of OS, EFS and CIR in the Non-HSCT in CR1 cohort were 37.5%, 19.9% and 75.6%, respectively. They were considered to be statistically significant. Of the 17 patients who relapsed during consolidation chemotherapy, 9 patients who underwent chemotherapy only (Non-HSCT after relapse cohort) all died within 44 months. For the remaining 8 patients who chose allo-HSCT (HSCT in CR2 cohort) when they achieved the second complete remission (CR2), the estimated 4-year probability of OS was 47.6% (P=0.002). Multivariate analysis showed that HSCT in CR1 was the only independent protective factor for OS, EFS and CIR, and age at diagnosis (≥10 years) was an independent risk factor of OS.

Conclusions: Allo-HSCT (especially haplo-HSCT) in CR1 may reduce the risk of relapse and improve prognosis in non-infant children with MLL-r B-ALL. In addition, allo-HSCT also seemed to be an effective approach to improve the prognosis of relapsed patients. Thus, haplo-HSCT could be an alternative approach for non-infant children with MLL-r B-ALL.