Maryam Mohebbi - Department of Pathology, Medical School, Shiraz University of Medical Sciences, Shiraz, Iran
Mansoureh Shokripour - Department of Pathology, Medical School, Shiraz University of Medical Sciences, Shiraz, Iran
Maral Mokhtari - Department of Pathology, Medical School, Shiraz University of Medical Sciences, Shiraz, Iran

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 hSNF۵/INI۱ gene in most of the cases. The INI۱ protein expression can be helpful for the accurate diagnosis.Methods: In this study, immunohistochemical staining  (IHC) using INI۱ antibody was performed to determine the possibility of ATRT misdiagnosis. Totally, ۱۴۷ tumors including ۶ ATRTs, ۸۱ medulloblastomas, and ۶۰ other CNS tumors were examined in children between ۰ and ۱۷ 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 INI۱ study. Additionally, two cases were recurrent tumors whose features were consistent with those of ATRT. The INI۱ immunostaining was negative in these cases.Conclusion: INI۱ was very helpful in distinguishing ATRT from its mimickers in challenging cases. All known ATRT cases in this study were immunonegative for INI۱. Thus, INI۱ 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.

ATRT, CNS tumors, High grade, INI۱, Pediatric