Central nervous system embryonal tumors with EWSR1-PLAGL1 rearrangements reclassified as INI-1 deficient tumors at relapse

Abstract Purpose Central nervous system (CNS) embryonal tumors are a diverse group of malignant tumors typically affecting pediatric patients that recently have been better defined, and this paper describes evolution of a unique type of embryonal tumor at relapse. Methods Two pediatric patients with CNS embryonal tumors with EWSR1-PLAGL1 rearrangements treated at Arkansas Children’s Hospital with histopathologic and molecular data are described. Results These two patients at diagnosis were classified as CNS embryonal tumors with EWSR1-PLAGL1 rearrangements based on histologic appearance and molecular data. At relapse both patient’s disease was reclassified as atypical teratoid rhabdoid tumor (ATRT) based on loss of INI-1, presence of SMARCB1 alterations, and methylation profiling results. Conclusion CNS embryonal tumors with EWSR1-PLAGL1 rearrangements acquire or include a population of cells with SMARCB1 alterations that are the component that predominate at relapse, suggesting treatment aimed at this disease component at diagnosis should be considered.