Evaluation of INI1 Protein Expression Through IHC Study in Pediatric High-Grade Brain Tumors in South of Iran in 2008-2021

BACKGROUND & OBJECTIVE: Brain tumors are the most frequent solid tumors in children. High-grade tumors are more challenging in diagnosis. Atypical teratoid rhabdoid tumor (ATRT) may be mistaken for other high-grade brain tumors. Molecular genetic analysis of ATRT has shown deletion and mutation in the hSNF5/INI1 gene in most of the cases. The INI1 protein expression can be helpful for the accurate diagnosis. METHODS: In this study, immunohistochemical staining (IHC) using INI1 antibody was performed to determine the possibility of ATRT misdiagnosis. Totally, 147 tumors including 6 ATRTs, 81 medulloblastomas, and 60 other CNS tumors were examined in children between 0 and 17 years old. RESULTS: No nuclear staining was found in the six ATRT cases, while most of other CNS tumors demonstrated nuclear staining. Five cases were previously diagnosed with medulloblastoma, primitive neuroectodermal tumor (PNET), and anaplastic oligodendroglioma, while the diagnoses were changed to ATRT based on the re-evaluation of the H&E slides and INI1 study. Additionally, two cases were recurrent tumors whose features were consistent with those of ATRT. The INI1 immunostaining was negative in these cases. CONCLUSION: INI1 was very helpful in distinguishing ATRT from its mimickers in challenging cases. All known ATRT cases in this study were immunonegative for INI1. Thus, INI1 is recommended to be used in the initial IHC panel for the high-grade brain tumors, especially in children under the age of three years, so that they can benefit from intensified therapeutic regimens.