A Rare Case of Pleural Epithelioid Mesothelioma With a Prominent Myxoid Stroma Reported With Morphology, Fluorescent In Situ Hybridization, and Ultrastructural Findings

Our plain-English summary of A Rare Case of Pleural Epithelioid Mesothelioma With a Prominent Myxoid Stroma Reported With Morphology, Fluorescent In Situ Hybridization, and Ultrastructural Findings, by H. Sonobe, R. Omote, T. Habara, et al (Curēus, 2024).

The study

• Authors: H. Sonobe, R. Omote, T. Habara, K. Washio, N. Yamazoe, S. Matsumoto, K. Nabeshima, H. Toda
• Journal: Curēus
• Published: 2024;16(6):e62212
• Type of article: Case report
• Read it: PubMed · Publisher · Free full text

Abstract

Herein, we report a rare case of pleural epithelioid malignant mesothelioma with a prominent myxoid stroma. To date, detailed morphological or molecular pathological findings have not been reported for this type of tumor. Hence, we aimed to describe the cytological, histological, immuno-cytohistological, electron-microscopic, and molecular pathological findings using fluorescence in situ hybridization (FISH) in such a case. The patient was a male in his mid-sixties with a history of asbestos exposure and had originally visited the hospital with a persistent cough and fever. Chest radiography revealed left pleural effusion, and laboratory examination revealed a high titer for hyaluronic acid in the effusion. Additionally, computed tomography revealed diffuse multinodular or cystic lesions in the left parietal pleura, and pleural effusion cytology revealed large epithelioid cells with mild nuclear atypia, which were considered reactive mesothelial cells. Cytologically, Giemsa staining revealed that these cells harbored variously sized intracytoplasmic vacuoles that were Alcian-blue-positive, suggesting hyaluronan production. Biopsy revealed large epithelioid cells that loosely proliferated against a prominent myxoid background. These cells were immuno-positive for calretinin, Wilms' tumor 1, D2-40, vimentin, and cytokeratin AE1/AE3 but not for carcinoembryonic antigen, Ber-EP4, or desmin. BRCA 1 associated protein 1 immunostaining showed nuclear loss, and FISH showed homozygous deletion of cyclin-dependent kinase inhibitor 2A (p16) on chromosome 9p21. Based on these findings, the lesion was diagnosed as an epithelioid mesothelioma with a prominent myxoid stroma. Electron-microscopy demonstrated a dense microvillus pattern on the surface of the tumor cells, indicating a mesothelial cell origin, and variously sized vacuoles in the cytoplasm, confirming the presence of intracytoplasmic vacuoles demonstrated on cytology. The tumor tissues obtained during surgery harbored prominent myxoid stroma, which proved that the present tumor was consistent with this type of mesothelioma. After informed consent was obtained, the patient and family wished for total resection of the tumor and postoperative chemotherapy, and the patient eventually died eight months after surgery.

Copyright © 2024, Sonobe et al.

In plain English

This case report describes one construction worker in his mid-sixties with a history of asbestos exposure. The case was seen in Fukuyama, Japan, over 10 years before the report. He had a persistent cough and fever, and fluid around his left lung. The fluid's hyaluronic acid was above 200,000 ng/ml. Fluid cells looked only mildly abnormal, so the authors first considered them reactive (non-cancerous) lining cells. A biopsy showed loosely scattered cells in an abundant jelly-like (myxoid) background. BAP1 protein staining was lost in tumor cell nuclei but kept in non-tumor cells. FISH genetic testing found a homozygous CDKN2A (p16) deletion in 15 of 59 counts (25.4%) and a heterozygous one in 29 of 59 (49.2%); the article does not say what was counted. Electron microscopy supported a mesothelial origin. The diagnosis was pleural epithelioid mesothelioma with a prominent myxoid stroma. The authors rated the tumor low grade and judged its outlook favorable. Even so, after surgery and ineffective chemotherapy, he died eight months after surgery. The authors concluded that BAP1 and FISH results confirmed mesothelioma and more cases are needed.

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 man, a construction worker in his mid-sixties with a history of asbestos exposure, referred to Chugoku Central Hospital (Fukuyama, Japan). The authors encountered the case more than 10 years before the report.
• Exposure: A history of asbestos exposure as a construction worker; the article gives no fiber type, products or dose
• Main results:
  • Hyaluronic acid in the patient's pleural effusion was abnormally elevated (more than 200,000 ng/ml)
  • On cytology of the pleural fluid, the authors initially considered the large epithelioid cells to be reactive mesothelial cells rather than tumor cells
  • On biopsy, the tumor cells were positive for calretinin, D2-40, WT1, EMA, CD146, cytokeratin AE1/AE3 and vimentin, and negative for CEA, Ber-EP4 and desmin
  • The tumor cells showed nuclear loss of BAP1, while non-tumor cells kept nuclear BAP1 staining
  • FISH for CDKN2A (p16) on chromosome 9p21 showed homozygous deletion in 25.4% (15/59) and heterozygous deletion in 49.2% (29/59). The article does not state what unit was counted.
  • Electron microscopy showed a highly microvillous cell surface. The authors stated that the FISH and electron-microscopic findings supported mesothelioma.
  • Under WHO 2021 criteria, the authors graded the tumor as nuclear grade I, with a low mitotic figure, no necrosis and a low overall tumor score. They judged it to have a favorable prognosis because of the abundant myxoid stroma.
  • The tumor was totally excised and treated with carboplatin and pemetrexed. Chemotherapy was stopped when it had no effect on progressive disease, and the patient died eight months after surgery.
• The authors' conclusion: The authors concluded that, although cytology suggested reactive cells, BAP1 nuclear loss and p16-FISH deletion confirmed mesothelioma. They added that more cases are needed to describe this tumor type in detail.

Topics

Medical terms in this study, explained in our Lexicon: Epithelioid, Mesothelioma, Myxoid Stroma, Fluorescence In Situ Hybridization (FISH), Asbestos Exposure, Pleural Effusion, Hyaluronic Acid, Parietal Pleura.

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• Fluorescence in situ hybridization detection of chromosome 22 monosomy in pleural effusion cytology for the diagnosis of mesothelioma — Y. Kinoshita, M. Hamasaki, et al. (2021)

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