SMARCB1/INI1-deficient undifferentiated tumour of the thorax - a case report and review of the literature

Sep 21, 2026

SMARCB1/INI1-deficient undifferentiated tumour of the thorax is presented as a rare high-grade entity showing undifferentiated morphology with loss of SMARCB1/INI1 expression, retention of SMARCA4 expression, and absence of NUT fusion protein. The case report describes the clinical presentation and pathological findings, then reviews the existing literature to contextualize this diagnosis within thoracic neoplasms. The authors argue for inclusion of this entity among heterogeneous thoracic undifferentiated tumours.

LanguageEnglish

CategoryHealthcare

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Case report

Summary

Introduction

Case presentation

PATHOLOGICA 2024;116:163-169; DOI: 10.32074/1591-951X-955 Received: December 13, 2023 Accepted: January 19, 2024 Correspondence Moreno Zagni [moreno.zagni@unimi.it](moreno.zagni@unimi.it) How to cite this article: Zagni M, Marando A, Negrelli M, et al. SMARCB1/INI1-deficient undifferentiated tumour of the thorax: a case report and review of the literaturer. Pathologica 2024;116:163-169 . [https://doi](https://doi). org/10.32074/1591-951X-955 © Copyright by Società Italiana di Anatomia Patologica e Citopatologia Diagnostica, Divisione Italiana della International Academy of Pathology OPEN ACCESS This is an open access journal distributed in accordance with the CC-BY-NC-ND (Creative Commons AttributionNonCommercial-NoDerivatives 4.0 International) license: the work can be used by mentioning the author and the license, but only for non-commercial purposes and only in the original version. For further information: [https://creativecommons](https://creativecommons). org/licenses/by-nc-nd/4.0/deed.en Case report SMARCB1/INI1-deficient undifferentiated tumour of the thorax: a case report and review of the literature Moreno Zagni1 , Alessandro Marando2 , Mariachiara Negrelli1 , Calogero Lauricella2 , Valentina Motta2 , Giulia Paglino2 , Silvio Veronese2 , Emanuele Valtorta2 , Emanuela Bonoldi2 , Giuseppe Pelosi1,3 1 Postgraduate School of Pathology, University of Milan, Milan, Italy; 2 Department of Surgical Pathology, Niguarda Hospital, Milano, Italy; 3 Department of Oncology and Hemato-Oncology, University of Milan, Milan, Italy; InterHospital Pathology Division, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) MultiMedica, Milan, Italy Summary The 5th WHO classification of thoracic tumours includes thoracic SMARCA4-deficient undifferentiated tumour (SMARCA4-UT) among the “other epithelial tumours of the lung”chapter. Herein, we present a case of undifferentiated thoracic neoplasm with retention of SMARCA4 expression, lack of NUT fusion protein and loss of SMARCB1/INI1 expression. After presenting the clinical and pathological features of the tumour, we carried out areview of the literature on the same topic. Albeit very rare, we believe this entity should be included in the heterogeneous group of undifferentiated neoplasms of the thorax. Key words: SMARCB1-deficient undifferentiated tumour, SWI/SNF complex, thoracic undifferentiated tumours, SMARCA4-deficient undifferentiated tumour Introduction SMARCB1, also known as INI1, is a tumour suppressor gene located on chromosome 22 and is one of the subunits of the SWI/SNF chromatin remodelling complex, which plays a critical role in regulating gene expression and chromatin organization 1. Genomic alterations in SMARCB1 subunit, as in other SWI/SNF complex subunits such as SMARCA4, SMARCA2 and ARID1A, and their oncogenic implications have been long discussed. The 5th WHO classification of thoracic tumours includes thoracic SMARCA4-deficient undifferentiated tumour (SMARCA4-UT) among the “other epithelial tumours of the lung” chapter 2. These neoplasms are defined as high-grade malignant tumours showing undifferentiated and, less frequently, rhabdoid morphology and defective immunohistochemical expression of SMARCA4 (or BRG1). They typically involve themediastinum, lung and/or pleura with variable infiltration of the chest wall. SMARCA4-UT typically shows complete loss of SMARCA4 expression, even though nearly 25% of cases only exhibit only a reduced expression, which is frequently associated with SMARCA2 (or BRM) loss and SMARCB1 retention. Histologically, these neoplasms consist of solid proliferations of large and discohesive elements with variable pleomorphism and prominent nucleoli. Mitosis and necrosis are common and rhabdoid elements can also be identified. Immunohistochemically, they often show a focal and weak expression of cytokeratins, but some cases may be completely unreactive. Diffuse positivity for synaptophysin has been repor

FAQs

What molecular findings characterize the reported thoracic tumour?

The tumour shows retention of SMARCA4 expression, lack of NUT fusion protein, and loss of SMARCB1/INI1 expression.

How does the article position this entity within WHO thoracic tumour classification?

It contrasts with SMARCA4-deficient undifferentiated tumour and argues that, despite rarity, the described SMARCB1/INI1-deficient case should be included among heterogeneous undifferentiated tumours of the thorax.

What was the patient’s presenting symptom in the case report?

The patient was referred for recurring episodes of haemoptysis.

Sep 21, 2026

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