Novel SMARCA4 Variant in an Infant With Atypical Teratoid Rhabdoid Tumor

Atypical teratoid/rhabdoid tumors (AT/RT) are malignant central nervous system (CNS) tumors. Typically, AT/RT is classified as SMARCB1 (INI-1) deficient or as SMARCA4 (BRG1) deficient. In this case, we describe a unique case of AT/RT with a novel SMARCA4 missense variant identified on next-generation sequencing but retained expression of INI-1 and BRG-1 on immunohistochemistry. Diagnosis of the tumor and discovery of the novel SMARCA4 variant was only possible after comprehensive tumor molecular testing tailored for pediatric malignancies. This case highlights the importance of molecular genetic testing as part of a workup in neoplasms concerning for possible AT/RT.