Erythroblastic Sarcoma in Adults and Children: Different Pathways to the Same Destination.

Erythroblastic sarcoma (ES), the mass-forming presentation of acute erythroid leukemia, is a rare and challenging diagnosis. Given the limited number of published cases, the diagnostic criteria, immunophenotype, and molecular characteristics are not well defined. We describe 56 cases of ES (36 adult and 11 pediatric cases from our cohort, and 9 pediatric cases from the literature). The median age was 60 years among adults and 1.8 years among children. An association with prior cytotoxic therapy or myeloid neoplasm was documented in 10/36 (28%) and 25/36 (69%) adults, respectively, but was not reported in children. Bones were the most common site of involvement among adults (16/36, 44%), whereas soft tissue or central nervous system involvement was most common among children (each 9/20, 45%). Adult and pediatric ES shared similar morphologic features with all cases showing mass formation of erythroblasts and/or involvement of body fluids. Immunophenotypic analysis showed that blasts were positive for CD71 (49/49, 100%), GLUT1 (12/12, 100%), CD43 (37/39, 95%), E-cadherin (38/44, 86%), and CD117 (39/51, 76%) but were mostly negative for CD45 (15/48, 31% positive). Strong and diffuse P53 expression was common among adults (21/24, 88%) and absent among children (3/10, 30% with dim/subset positivity). Although a complex karyotype was common in adult (15/17, 88%) and pediatric ES (8/12, 68%), TP53 mutations were exclusively seen in adult ES (17/19, 89%), at least 11 of which (65%) were biallelic. Instead, pediatric ES was enriched for gene fusions; specific fusions were identified in 10 cases, 7 of which involved NFIA rearrangement. The prognosis was poor among both age groups; 29/37 (78%) patients died from disease with a median overall survival of 3 months. Overall, these results show that adult and pediatric ES have overlapping morphologic and immunophenotypic features but distinct molecular profiles suggesting diverging pathogenesis.