Differential Diagnosis of Malignant Pleural Mesothelioma on Cytology: A Gene Expression Panel versus BRCA1-Associated Protein 1 and p16 Tests

Our plain-English summary of Differential Diagnosis of Malignant Pleural Mesothelioma on Cytology: A Gene Expression Panel versus BRCA1-Associated Protein 1 and p16 Tests, by R. Bruno, G. Alì, A.M. Poma, et al (The Journal of Molecular Diagnostics, 2020).

The study

• Authors: R. Bruno, G. Alì, A.M. Poma, A. Proietti, R. Libener, N. Mariani, C. Niccoli, A. Chella, A. Ribechini, F. Grosso, G. Fontanini
• Journal: The Journal of Molecular Diagnostics
• Published: 2020;22(4):457-466
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Pleural effusions are among the first clinical manifestations of malignant pleural mesothelioma (MPM) and often constitute the only available material for diagnosis. Although an MPM diagnosis can be reliable on cytology, the reported sensitivity is low (30% to 75%). Particularly, it can be hard to discriminate epithelioid MPM, the most common histotype, from reactive mesothelial hyperplasia (MH). Currently, BRCA1-associated protein 1 (BAP1) and CDKN2A (p16), evaluated by immunohistochemistry and fluorescent in situ hybridization, respectively, are the most valuable markers to discriminate MPM and MH. Both markers have a high specificity, but their sensitivity is not always satisfying, even when used together. We have recently developed a 117-gene expression panel, based on Nanostring technology, able to differentiate epithelioid MPM from MH pleural tissues better than BAP1 and p16. Herein, we evaluated the efficacy of the same panel on an independent retrospective cohort of 23 MPM and 11 MH pleural effusions (cell blocks and smears). The overall sensitivity and specificity of the panel were equal to 0.9565 and 1, respectively. Moreover, the panel performance was compared with BAP1 and p16 on 25 cell blocks. Sensitivity levels of gene panel, BAP1 alone, p16 alone, and BAP1 plus p16 were 1, 0.5882, 0.4706, and 0.7647, respectively. Specificity was always 1. Although further validation is needed, this gene panel could really facilitate patients' management, allowing a definitive MPM diagnosis directly on pleural effusions.

Copyright © 2020 Association for Molecular Pathology and American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.

In plain English

This Italian study used archived pleural fluid samples from 23 patients with epithelioid malignant pleural mesothelioma (MPM) and 11 with benign reactive mesothelial hyperplasia (MH). It tested whether a 117-gene panel the authors had developed earlier could tell the two apart. Across all 34 samples, sensitivity was 0.9565 (95% confidence interval 0.8696 to 1) and specificity was 1 (0.7273 to 1). One MPM sample was misclassified as benign. On 25 cell blocks (17 MPM, 8 MH), the panel was compared with BAP1 and p16 tests. Sensitivity was 1 (1 to 1) for the panel, 0.5882 (0.3529 to 0.8235) for BAP1, 0.4706 (0.2353 to 0.7059) for p16, and 0.7647 (0.5294 to 0.9412) for both combined. Specificity was 1 for every method, with intervals of 1 to 1 for the panel, 0.6364 to 1 for BAP1, 0.6923 to 1 for p16 and 0.5000 to 1 for the combination. Four MPM cases showed neither BAP1 loss of expression nor p16 deletion, and the panel classified all four as malignant. The authors concluded that the panel could allow an earlier, definitive diagnosis on pleural fluid. They stated that it could not yet replace current tests and needed prospective validation. Asbestos exposure was not studied.

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: Retrospective diagnostic accuracy study: validation of a gene expression panel on an independent cohort of archived cytology samples, compared with BAP1 immunohistochemistry and p16 FISH
• Who was studied: Archived pleural effusion samples from 23 patients with epithelioid MPM (17 cell blocks, 6 smears; median age 68) and 11 patients with reactive mesothelial hyperplasia (10 cell blocks, 1 smear; median age 60). The samples came from the University Hospital of Pisa and SS Antonio and Biagio General Hospital of Alessandria, Italy. Collection dates are not given.
• Exposure: No asbestos exposure was assessed. The study evaluated three diagnostic tests: a 117-gene expression panel (Nanostring technology), BAP1 immunohistochemistry, and p16 (CDKN2A) deletion by FISH.
• Main results:
  • Across all 34 cytology samples, the gene panel had a sensitivity of 0.9565 (95% CI, 0.8696 to 1) and a specificity of 1 (95% CI, 0.7273 to 1).
  • All samples were correctly classified except one MPM case, a smear that the panel classified as benign. Its paired surgical tissue sample was correctly classified as malignant.
  • On the 25 cell blocks tested with all methods (17 MPM, 8 MH), BAP1 expression was lost in 10 of 17 MPMs and p16 was deleted in 9 of 17 MPMs. All MH cases retained BAP1 and showed no p16 deletion.
  • On the 25 cell blocks, sensitivity was 1 (95% CI, 1 to 1) for the gene panel, 0.5882 (0.3529 to 0.8235) for BAP1, 0.4706 (0.2353 to 0.7059) for p16, and 0.7647 (0.5294 to 0.9412) for BAP1 plus p16.
  • On the 25 cell blocks, specificity was 1 for each method. The 95% CIs were 0.6364 to 1 for BAP1, 0.6923 to 1 for p16, 0.5000 to 1 for BAP1 plus p16, and 1 to 1 for the panel.
  • Four of 17 MPM cases (23.5%) showed neither BAP1 loss of expression nor p16 deletion, and the gene panel classified all four as malignant.
  • Comparing the 23 epithelioid MPM effusions with the 11 MH effusions, 32 genes were up-regulated and 10 were down-regulated in the MPM samples.
• The authors' conclusion: The authors concluded that the panel could give MPM patients a definitive and earlier diagnosis directly on pleural effusions, avoiding invasive procedures. They also stated that it could not yet replace IHC and FISH tests, but could be considered when the diagnostic algorithm was uninformative.
• Limitations the authors state:
  • The panel needs further, prospective validation, and its cost-effectiveness compared with current tests has yet to be established.
  • Only epithelioid MPM was tested, so how the panel performs for other MPM subtypes and other pleural conditions is unknown.
  • The minimum tumor cell content needed for the assay to be informative has not been determined.
  • There was not enough material to also perform MTAP and EZH2 immunohistochemistry.
  • BAP1 and p16 testing was not done on smears. Two cell blocks could not be tested because too few tumor cells remained, so the comparison was limited to 25 cell blocks.
  • The one disagreement between cytology and tissue indicated to the authors that this analysis is more robust on tissue samples. They also noted that cytology samples can be affected by low cellularity, bleeding and inflammation.

Topics

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

Medical terms in this study, explained in our Lexicon: Differential Diagnosis, Pleural Mesothelioma, Cytology, Pleural Effusion, Epithelioid, Reactive Mesothelial Hyperplasia, BAP1, CDKN2A.

Related studies

• The value of BRCA-1-associated protein 1 expression and cyclin-dependent kinase inhibitor 2A deletion to distinguish peritoneal malignant mesothelioma from peritoneal location of carcinoma in effusion cytology specimens — W. Althakfi, S. Gazzo, et al. (2020)
• Usefulness of methylthioadenosine phosphorylase and BRCA-associated protein 1 immunohistochemistry in the diagnosis of malignant mesothelioma in effusion cytology specimens — K.B. Berg, A.M. Churg, et al. (2020)
• The "Brescia panel" (Claudin-4 and BRCA-associated protein 1) in the differential diagnosis of mesotheliomas with epithelioid features versus metastatic carcinomas — L. Bernardi, T. Bizzarro, et al. (2021)
• Diagnostic value of BRCA1-associated protein-1, glucose transporter-1 and desmin expression in the discrimination between reactive mesothelial proliferation and malignant mesothelioma in tissues and effusions — S. Önder, E. Özogul, et al. (2019)
• BAP1 immunohistochemistry and p16 FISH results in combination provide higher confidence in malignant pleural mesothelioma diagnosis: ROC analysis of the two tests — T. Hida, M. Hamasaki, et al. (2016)
• Loss of BRCA1-associated protein 1 (BAP1) expression is useful in diagnostic cytopathology of malignant mesothelioma in effusions — I. Cozzi, F.A. Oprescu, et al. (2018)

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