Diagnostic use of muscle markers in the cytologic evaluation of serous fluids

Our plain-English summary of Diagnostic use of muscle markers in the cytologic evaluation of serous fluids, by A.M. Afify, B.M. Al-Khafaji, A.F. Paulino, et al (Applied Immunohistochemistry & Molecular Morphology, 2002).

The study

• Authors: A.M. Afify, B.M. Al-Khafaji, A.F. Paulino, R.M. Davila
• Journal: Applied Immunohistochemistry & Molecular Morphology
• Published: 2002;10(2):178-82
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Differentiating reactive mesothelial cells from malignant mesotheliomas and from adenocarcinomas can be diagnostically challenging when based solely on the morphologic examination of serous fluids. The diagnosis even after the use of standard immunohistochemical stains may at times be inconclusive because of the variable reactivity of mesothelial cells for these markers. Pathologists and cytologists underutilize reactivity for desmin, a feature of mesothelial cells apparently not shared by adenocarcinomas. The purpose of this study was to evaluate the extent to which mesothelial cells express muscle differentiation and to assess the diagnostic utility of muscle markers in distinguishing reactive mesothelial cells from malignant mesotheliomas and adenocarcinomas. Archival paraffin-embedded cell blocks of serous fluids from 24 cases of reactive mesothelial cells, 14 cases of malignant mesothelioma, and 56 cases (14 cases from each) of metastatic adenocarcinoma from the lung, breast, ovary, and gastrointestinal tract were retrieved. Five cases of omentum with unremarkable mesothelial cells were also included in the study. All cases were stained for desmin, actin, myoglobin, and myogenin and evaluated independently by two observers. Strong cytoplasmic reactivity for desmin was noted in 22 of 24 cases (92%) of reactive mesothelial cells. The reactive mesothelial cells did not express actin, myoglobin, or myogenin. All cases of malignant mesothelioma and metastatic adenocarcinoma were negative for the four muscle markers. The mesothelial lining and scattered subserosal cells in the omental sections were positive for desmin. Because desmin was expressed only in benign mesothelial cells, it may serve as a reliable marker in distinguishing reactive mesothelial cells from mesothelioma or from adenocarcinoma. Awareness of this staining pattern is also important to avoid pitfalls when evaluating body fluid specimens from patients with a history of tumors expressing muscle differentiation.

In plain English

This laboratory study tested whether stains for muscle proteins can help pathologists tell apart three kinds of cells found in fluid around the lungs or in the abdomen: non-cancerous reactive mesothelial cells, malignant mesothelioma, and cancer spread from elsewhere (metastatic adenocarcinoma). The authors used stored samples from the University of Michigan Hospitals: 94 cases (24 with reactive mesothelial cells, 14 with malignant epithelioid mesothelioma, and 14 each of adenocarcinoma spread from the lung, breast, ovary and gastrointestinal tract) plus 5 samples of omentum, a fatty tissue in the abdomen. These were stained for desmin, actin, myoglobin and myogenin. Desmin was positive in 22 of 24 reactive mesothelial cell cases (92%). Reactive mesothelial cells did not stain for the other three markers. All mesothelioma and adenocarcinoma cases were negative for all four markers. The authors concluded that desmin may serve as a reliable marker for separating reactive mesothelial cells from mesothelioma or adenocarcinoma. They noted that their rules for calling a stain positive may have been stricter than other researchers' rules, and that other forms of mesothelioma should be studied. The study did not look at asbestos exposure.

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: Laboratory (immunohistochemistry) study of archival pathology samples, evaluating diagnostic markers
• Who was studied: Cell blocks of body fluids from 94 cases at the University of Michigan Hospitals, Ann Arbor: 24 reactive mesothelial cells and 14 each of malignant epithelioid mesothelioma and metastatic lung, breast, ovarian and gastrointestinal adenocarcinoma (53 from ascitic fluid, 41 from pleural effusions), plus 5 cases of unremarkable omentum. Dates of the cases were not given.
• Exposure: No asbestos or other environmental exposure was studied. The study tested four muscle-marker stains: desmin, actin, myoglobin and myogenin. A case counted as positive if at least 20% of cells stained with 2+ to 4+ intensity.
• Main results:
  • Desmin was positive in 22 of 24 cases (92%) that contained only reactive mesothelial cells.
  • Reactive mesothelial cells did not express actin, myoglobin or myogenin.
  • All malignant mesothelioma cases and all metastatic adenocarcinoma cases were negative for all four muscle markers.
  • Reactive mesothelial cells seen alongside the tumor cells in the cancer cases were also desmin positive.
  • In the omentum sections, the mesothelial cell lining and scattered subserosal cells stained strongly for desmin.
• The authors' conclusion: The authors concluded that, because desmin was expressed only in benign mesothelial cells, it may serve as a reliable marker for distinguishing reactive mesothelial cells from mesothelioma or adenocarcinoma. They suggested using it together with other markers.
• Limitations the authors state:
  • The authors' criteria for calling a stain positive may differ from, and be stricter than, those used by other researchers, some of whom found desmin in mesotheliomas.
  • Only epithelioid mesotheliomas were studied. The authors said other forms of mesothelioma need study to validate the results.

Topics

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

Medical terms in this study, explained in our Lexicon: Serous Fluid, Reactive Mesothelial Cells, Malignant Mesothelioma, Adenocarcinoma, Mesothelial Cells, Desmin, Cell Block, Omentum.

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• Distribution of transforming growth factor-beta 1, fibronectin, and smooth muscle actin in asbestos-induced pulmonary fibrosis in rats — T.D. Perdue, A.R. Brody (1994)
• Multiple skeletal muscle metastases from malignant pleural mesothelioma — W. Grellner, M. Staak (1995)
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• Smooth muscle tumours of the pleura — A.R. Gibbs (1995)

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