Pre- and post-transplant extramedullary involvement in adult patients with t(8;21)(q22;q22) acute myeloid leukemia: incidence, risk factors and outcomes.

The risk factors and prognostic impact of extramedullary involvement (EMI) before and after allogeneic hematopoietic stem-cell transplantation (allo-HSCT) in t(8;21)(q22;q22) acute myeloid leukemia (AML) remain inconclusive. We performed a multicenter retrospective study including 560 t(8;21) AML patients from 15 Chinese hematology centers. KIT mutations were more frequently observed in patients with EMI at diagnosis. EMI at diagnosis was not an independent risk factor for overall survival (OS) after adjustment for KIT mutations. The 3-year post-transplant OS rates between isolated extramedullary relapse (EMR) and bone marrow relapse after allo-HSCT were comparable. Chronic graft-versus-host disease (cGVHD) was associated with increased incidence of isolated EMR (HR = 2.33, p = 0.048). Pre- and post-transplant minimal residual disease (MRD), measured by RUNX1-RUNX1T1 transcript levels, showed no significant association with isolated EMR. In conclusion, EMI at diagnosis may not significantly impact survival in t(8;21) AML. For patients with cGVHD after allo-HSCT, EMR should be monitored.