# Atypical Teratoid/Rhabdoid Tumor with Retained SMARCB1 (INI1) Expression and Rare SMARCA4 Gene Mutation: A Case Report of a Pediatric Patient

## TL;DR

This case report describes a rare pediatric brain tumor with preserved INI1 protein expression and a rare SMARCA4 gene mutation, highlighting unusual genetic features and aggressive disease progression.

## Contribution

The paper presents a rare case of AT/RT with retained SMARCB1 expression and a novel SMARCA4 mutation, expanding understanding of tumor genetic diversity.

## Key findings

- The tumor showed classical rhabdoid features but retained INI1 expression, which is atypical for AT/RT.
- A heterozygous frameshift mutation in the SMARCA4 gene was identified as the genetic basis of the tumor.
- The patient's condition worsened despite treatment, indicating the aggressive nature of this tumor variant.

## Abstract

Atypical teratoid/rhabdoid tumors (AT/RT) are highly aggressive tumors of the central nervous system (CNS), accounting for 1–3% of all pediatric CNS tumors. In general, AT/RTs are associated with biallelic inactivation of SMARCB1, resulting in the loss of expression of the integrase interactor 1 (INI1) protein. In this report, we describe the clinical course of an infant patient who presented with fatigue, postprandial vomiting, and disability of left side movement. Histological examination revealed classical features indicative of rhabdoid tumors, yet an atypical immunohistochemical profile with preserved INI1 expression was observed. Molecular diagnostics further elucidated the presence of a heterozygous frameshift variant, SMARCA4 c.2693del, p.(Asn898Thrfs*12), underscoring the distinctive genetic foundations of the case. Surgical resection of the tumor was administered with subsequent chemotherapy to the patient, but the condition worsened dynamically, and a decision was made to give the patient palliative therapy. We report on a patient with AT/RT caused by a rare mutation of the SMARCA4 gene and an aggressive course of disease to provide more information and characteristics of these tumors.