Extramedullary leukemia in children with acute myeloid leukemia: A population-based cohort study from the Nordic Society of Pediatric Hematology and Oncology (NOPHO)

Background: The prognostic significance of extramedullary leukemia (EML) in childhood acute myeloid leukemia is not clarified. Procedure: This population-based study included 315 children from the NOPHO-AML 2004 trial. Results: At diagnosis, 73 (23%) patients had EML: 39 (12%) had myeloid sarcoma, 22 (7%) had central nervous system disease, and 12 (4%) had both. EML was associated with young age (median age: 2.6 years), a high white blood cell count (median: 40 x 10(9)/l), M5 morphology (40%), and 11q23/MLL (KMT2A) rearrangements (34%). No patient received involved field radiotherapy. Five-year event-free survival did not differ significantly between the EML and the non-EML patients (54% vs. 45%, P = 0.57), whereas 5-year overall survival (OS) was significantly lower in the EML group (64% vs. 73%, P = 0.04). The risk of induction death was significantly higher for EML patients (8% vs. 1%, P = 0.002). There was a trend toward a lower risk of relapse for EML patients (5-year cumulative incidence of relapse 33% vs. 49%, P = 0.16). Traumatic lumbar puncture did not adversely affect survival in this cohort. Conclusions: EML was associated with increased risk of induction death impacting the OS. No patients relapsed at the primary site of the myeloid sarcoma despite management without radiotherapy.