Clinical characteristics and prognostic significance of extramedullary involvement in childhood acute myeloid leukemia

Background. Extramedullary infiltration (EI) is relatively common in children with acute myeloid leukemia (AML) (up to 20-25 %). However, its clinical and prognostic significance remains poorly understood.Objective: to describe clinical features and to define prognostic significance of EI in children with AML.Materials and methods. The subjects of retrospective observational study were 228 children with de novo AML. The median age was 6.6 years. All of them were treated according to the protocol AML-MM-2006 from April 2007 to June 2018.All patients with EI were divided into three cohorts according to the localization of the lesions: 1) central nervous system (CNS) involvement (CNS group), 2) other localizations apart from CNS (myelosarcomas (MS) group), 3) combined lesions (CNS + MS group).Results. EI was diagnosed in 84 patients (36.84 %) with de novo AML. Among them 47 (55.95 %) had CNS involvement, 20 (23.81 %) had MS, 15 (17.86 %) had both CNS involvement and MS. 5-year overall survival (OS) rate was slightly higher in patients with CNS involvement than in children without EI - 80 ± 12 % vs 71 ± 9 %, p = 0.26, however OS in patients with MS was significantly lower - 45 ± 16 % vs 71 ± 9 %, p <0.001. In addition, OS in high-risk patients according to the protocol AML-MM-2006 who underwent allogenic hematopoietic stem cell transplantation (HSCT) without EI and with MS (± CNS involvement) was similar to OS in main groups - 81 ± 11 % and 42 ± 26 % respectively, p = 0.004. 5-year event-free survival in patients with MS was also lower than in children without EI - 38 ± 16 % vs 51 ± 8 %, p = 0.011.Conclusion. Patients with MS had worse 5-year OS and EFS than children without EI according to our study. Moreover allogenic HSCT conducted in first clinical remission did not improve the survival rate. Neuroleukemia as the only EI was not an unfavorable prognostic factor in our cohort of AML patients and was more often associated with inv(16).