Expression of muscle actins in diffuse mesotheliomas

Our plain-English summary of Expression of muscle actins in diffuse mesotheliomas, by I.T. Kung, V. Thallas, E.J. Spencer, et al (Human Pathology, 1995).

The study

• Authors: I.T. Kung, V. Thallas, E.J. Spencer, S.M. Wilson
• Journal: Human Pathology
• Published: 1995;26(5):565-70
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Ultrastructural examinations have shown myofibroblastoid differentiation in sarcomatoid/desmoplastic mesotheliomas, but immunohistochemical expression of muscle actins seldom has been documented. We examined 10 sarcomatoid, 12 epithelial, and five biphasic mesotheliomas immunohistochemically for the expression of muscle-specific actin (MSA) and smooth muscle actin (SMA) and compared it with that in 12 specimens of lung cancer. All of the sarcomatoid mesotheliomas were found to be positive for both MSA and SMA. The epithelial cells in nine epithelial and two biphasic mesotheliomas were positive for MSA, but SMA was only positive in one epithelial mesothelioma. Conversely, the lung cancers were negative for both MSA and SMA in the epithelial cells, except for one specimen that was weakly positive for MSA. The stromal cells in both the epithelial mesotheliomas and lung cancers were negative for cytokeratin but were positive for MSA and SMA, whereas the sarcomatoid and biphasic mesothelioma spindle cells were positive for all three antibodies. We concluded that sarcomatoid mesothelioma was positive for MSA and SMA, which is in support of its myofibroblastic differentiation, and that positivity for MSA in some epithelial mesotheliomas might be of diagnostic value in differentiation from lung cancers.

In plain English

This laboratory study from a hospital pathology department in Victoria, Australia, used immunostaining to test diffuse mesothelioma tissue for two muscle-type proteins: muscle-specific actin (MSA) and smooth muscle actin (SMA). The authors examined stored tissue from 27 mesotheliomas (10 sarcomatoid/desmoplastic, 12 epithelial and five biphasic). For comparison, they also examined 12 lung cancers. The article does not discuss asbestos exposure. All 10 sarcomatoid/desmoplastic tumors stained positive for both MSA and SMA. Tumor cells in nine of the 12 epithelial mesotheliomas stained for MSA, and SMA was weakly and patchily positive in tumor cells of one. Tumor cells in the lung cancers were negative for MSA in all but one of the 12 specimens. Benign fibrous plaques seen in four specimens stained the same way as the sarcomatoid/desmoplastic tumors. The authors concluded that the results support muscle-like (myofibroblastic) features in sarcomatoid mesothelioma. They also concluded that MSA staining in some epithelial mesotheliomas might help tell them apart from lung cancer. They noted that the study was limited by its small number of cases.

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 archived tumor tissue (pathology case series with lung cancer comparison specimens)
• Who was studied: 27 diffuse mesotheliomas (10 sarcomatoid/desmoplastic, 12 epithelial, 5 biphasic) from the surgical and autopsy files of the Department of Anatomical Pathology, Heidelberg Repatriation Hospital, Victoria, Australia. For comparison: 12 lung carcinomas (8 adenocarcinomas, 2 squamous cell, 1 small cell, 1 large cell) and one solitary fibrous pleural tumor. Dates of cases not given.
• Main results:
  • All 10 sarcomatoid/desmoplastic mesotheliomas were positive for cytokeratin, SMA and MSA, and variably positive for vimentin. The Results text calls the staining strong. Table 2, as far as it is legible, grades it differently: MSA strong in five and moderate in five, and SMA strong in four, moderate in five and weak in one.
  • In the 12 epithelial mesotheliomas, MSA stained the stromal cells in all specimens and the epithelial (tumor) cells in 9 of 12 specimens.
  • In epithelial mesotheliomas, SMA was weakly and patchily positive in the epithelial cells in one specimen.
  • In the 5 biphasic mesotheliomas, the spindle cells were consistently positive for the muscle actins. The epithelial cells were negative for SMA but weakly positive for MSA in two specimens.
  • In the 12 lung cancers, the staining pattern was similar to the epithelial mesotheliomas, except that the cancer epithelial cells were negative for MSA in all but one specimen.
  • Benign fibrous plaques found in the sections of four specimens (two epithelial, two sarcomatoid/desmoplastic) stained the same way as the sarcomatoid/desmoplastic tumors and could be distinguished only by nuclear morphology.
  • The solitary fibrous pleural tumor was strongly positive for vimentin, MSA and desmin but negative for cytokeratin and SMA.
• The authors' conclusion: The authors concluded that sarcomatoid mesothelioma was positive for MSA and SMA, supporting its myofibroblastic differentiation. They also concluded that MSA positivity in some epithelial mesotheliomas might be of diagnostic value in distinguishing them from lung cancers.
• Limitations the authors state:
  • The authors stated that the study is limited by the small number of cases available.
  • The authors stated that muscle actin staining does not help distinguish a fibrous plaque from a sarcomatoid/desmoplastic mesothelioma.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Sarcomatoid, Desmoplastic Mesothelioma, Biphasic Mesothelioma, Lung Cancer, Spindle Cell.

Related studies

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• The serratus anterior muscle on chest radiographs — D. Gilmartin (1979)
• Actin-containing microfilaments of pulmonary epithelial cells provide a mechanism for translocating asbestos to the interstitium — A.R. Brody, L.H. Hill, et al. (1983)
• Actin polymerization plays a significant role in asbestos-induced inflammasome activation in mesothelial cells in vitro — M. MacPherson, C. Westbom, et al. (2017)
• Diagnostic use of muscle markers in the cytologic evaluation of serous fluids — A.M. Afify, B.M. Al-Khafaji, et al. (2002)

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