Extramedullary Relapse of Acute Leukemia after Haploidentical Hematopoietic Stem Cell Transplantation: Incidence, Risk Factors, Treatment, and Clinical Outcomes

• We examined extramedullary relapse (EMR) after haploidentical transplantation.
• The incidence of EMR was 4.0% at 3 years, higher in acute lymphoblastic leukemia.
• Disease status and chronic graft-versus-host disease were associated with EMR.
• Graft-versus-leukemia effect may help to prevent post-transplant EMR.

We examined the incidence, risk factors, treatment, and clinical outcomes of extramedullary relapse (EMR) in 961 acute leukemia patients undergoing HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT) between 2002 and 2013. Multiple control subjects were selected at random from the same cohort and matched to EMR cases for diagnosis, disease status at HSCT, age at the time of the HSCT, and year of HSCT. Forty patients exhibited EMR, with a median time to EMR of 207 days. The cumulative incidence of EMR was 4.0% at 3 years, and the incidence was higher in acute lymphoblastic leukemia patients compared with acute myeloid leukemia patients (5.6% versus 2.4%). In the multivariate analysis, non–complete remission (CR) status at HSCT (hazard ratio [HR] = 4.6; P = .018) and non–chronic graft-versus-host disease after HSCT (HR = 3.2; P < .001) were the independent risk factors for EMR after haplo-HSCT. Twenty-seven patients received combination treatments, and the proportion of patients who achieved CR was higher than those who received single treatment. Multifocal involvement at EMR (HR = 2.7; P = .024) and non-CR after EMR treatments (HR = 4.6; P < .001) were the independent risk factors for poor survival rates among EMR patients. We found that graft-versus-leukemia effect may help to prevent EMR after haplo-HSCT.