Cytopathologic Features of Metastatic Malignant Mesothelioma With SMARCB1 (INI-1) Deficient Diagnosed by Ultrasound-Guided Fine-Needle Aspiration: A Case Report

Our plain-English summary of Cytopathologic Features of Metastatic Malignant Mesothelioma With SMARCB1 (INI-1) Deficient Diagnosed by Ultrasound-Guided Fine-Needle Aspiration: A Case Report, by J. Yang, J. Liu, J. Jin, et al (Diagnostic Cytopathology, 2026).

The study

• Authors: J. Yang, J. Liu, J. Jin, D. Pan, L. Shao
• Journal: Diagnostic Cytopathology
• Published: 2026;54(4):E87-E92
• Type of article: Case report
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is a rare yet aggressive neoplasm that arises from mesothelial cells lining the thoracic and abdominal cavities, the pericardium, and the tunica testis. Characterized by rapid progression, high invasiveness, and a poor prognosis, MM poses significant clinical challenges. SMARCB1, also referred to as INI-1, hSNF5, or BAF47, is located on chromosome 22q11.2 and serves as a critical subunit of the SWI/SNF chromatin remodeling complex. INI-1 functions as a tumor suppressor and plays a vital role in DNA damage repair and regulation of cell growth. Case Presentation: A 37-year-old Chinese male with no history of asbestos exposure but a 10-year smoking history (30 cigarettes per day) presented with a cough lasting one month and a fever persisting for one day. Computed tomography (CT) showed multiple enlarged supraclavicular lymph nodes measuring up to 30 × 15 mm bilaterally. An ultrasound-guided fine-needle aspiration (FNA) of the left supraclavicular lymph nodes was subsequently performed. The SurePath-prepared liquid-based cytopathology (LBC) using Papanicolaou-staining revealed tumor cells organized in clusters with indistinct borders. The cells exhibited abundant cytoplasm and pleomorphic round nuclei, which displayed prominent nucleoli and mitotic activity. Additionally, scattered lymphoid fragments were observed in the background. The FNA sample was formalin-fixed and paraffin-embedded for cell block; 4-μm thick sections were prepared. Histological examination using HE-stained cell block revealed a solid sheet-like tumor growth characterized by minimal stroma and the absence of fibrovascular cores. The neoplastic cells had well-defined borders, abundant eosinophilic (partially clear) cytoplasm, and round-to-oval nuclei displaying focal atypia, finely dispersed chromatin, and prominent nucleoli. Immunohistochemistry (IHC) demonstrated positive staining for CK(pan), calretinin, D2-40, and SMARCA4, whereas NapsinA, TTF-1, P40, NUT, and WT-1 yielded negative results. The confirmed loss of INI-1 expression ultimately led to the diagnosis of metastatic INI-1 deficient MM. Conclusion: This case highlights the cytomorphological features and immunophenotype of INI-1 deficient MM diagnosed through FNA. An accurate diagnosis requires a thorough clinicopathological correlation and a comprehensive IHC panel.

© 2025 The Author(s). Diagnostic Cytopathology published by Wiley Periodicals LLC.

In plain English

This article is a case report about one patient. A 37-year-old Chinese man with no history of asbestos exposure and a 10-year smoking history went to hospital with a cough of one month and a fever of one day. Blood tumor markers were raised, including Ca-125 at 6316.9 U/mL. CT scans showed multiple enlarged lymph nodes, the largest about 30 by 15 mm, in the left side of the chest and above the left collarbone. Cells were taken from a lymph node above the left collarbone using an ultrasound-guided fine needle. Under the microscope the tumor cells formed clusters, had mostly round nuclei that varied markedly in appearance, and showed cell division. The cells stained positive for CK(pan), calretinin, D2-40 and SMARCA4. They stained negative for NapsinA, P40, TTF-1, NUT and WT-1, and had lost the INI-1 (SMARCB1) protein. The final diagnosis was metastatic malignant mesothelioma with INI-1 deficiency. The authors concluded that diagnosing this very rare tumor requires combining clinical findings, microscope findings and a panel of key stains.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Case report (single patient)
• Who was studied: One 37-year-old Chinese man with no history of asbestos exposure, evaluated in Zhejiang, China
• Exposure: No asbestos exposure was reported. The patient had a 10-year history of smoking, about 30 cigarettes per day.
• Main results:
  • Serum tumor markers in the patient were raised: Ca-125 at 6316.9 U/mL and Cyfra21-1 at 6.55 ng/mL
  • CT showed multiple enlarged lymph nodes up to about 30 × 15 mm in the left hilum, the mediastinum, next to the aortic arch and above the left clavicle
  • Fine-needle aspiration cytology showed clustered tumor cells with abundant cytoplasm and predominantly round nuclei showing marked pleomorphism (marked variation in appearance), prominent nucleoli and mitotic figures
  • The cell block showed solid sheet-like tumor growth with little stroma and no fibrovascular core
  • Tumor cells were positive for CK(pan), calretinin, D2-40 and SMARCA4, negative for NapsinA, P40, TTF-1, NUT and WT-1, and showed loss of INI-1 nuclear staining
  • Final diagnosis: metastatic malignant mesothelioma with INI-1 deficiency
• The authors' conclusion: The authors concluded that, because this entity is extremely rare, accurate diagnosis needs a comprehensive workup combining clinical findings, histologic and cytologic assessment, and a panel of key immunohistochemistry markers.
• Limitations the authors state:
  • The authors state that the clinical and biological implications of INI-1 deficiency in mesothelioma remain largely unexplored because it is rare
  • The authors state that the prognostic impact of INI-1 loss in mesothelioma remains unclear

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Ultrasound, Fine-Needle Aspiration, Neoplasm, Mesothelial Cells, Pericardium, Prognosis, Asbestos Exposure.

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• "Dry" pleural mesothelioma successfully diagnosed on endobronchial ultrasound (EBUS)-guided transbronchial needle aspiration (TBNA) — F. Lococo, G. Rossi, et al. (2014)
• Endoscopic Ultrasound with Bronchoscope-Guided Fine Needle Aspiration for the Diagnosis of Paraesophageally Located Lung Lesions — I. Skovgaard Christiansen, J.C. Kuijvenhoven, et al. (2019)
• Advantages of thoracic ultrasound-guided fine-needle aspiration biopsy in lung cancer and mesothelioma — M. Sperandeo, L. Dimitri, et al. (2014)
• Endoscopic ultrasound-guided fine-needle aspiration from ascites and peritoneal nodules: A scoping review — V. Sharma, S.S. Rana, et al. (2017)

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