Mesotheliomas with small cell features: report of eight cases

Our plain-English summary of Mesotheliomas with small cell features: report of eight cases, by N.G. Ordóñez (Modern Pathology, 2012).

The study

• Author: N.G. Ordóñez
• Journal: Modern Pathology
• Published: 2012;25(5):689-98
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Mesotheliomas with small cell morphology are rare and only one study of such cases has been published. As a result of their rare occurrence, some investigators have cast doubt on the existence of such a histologic variant of mesothelioma. This investigator reports a series of eight cases of epithelioid mesothelioma with small cell features, all of which originated in the pleura. Seven of the patients were men and one was a woman. Four patients had a history of asbestos exposure. Histologically, four of the mesotheliomas were epithelioid and four biphasic. The proportion of small cells seen in these cases constituted 80 to 100% of the tumor included in the biopsy material and 15 to 20% of the tumor present in the pneumonectomy specimens. Immunoreactivity for calretinin, keratin 5/6, keratin 7, pan-keratin, WT1, podoplanin, and mesothelin was seen in all cases tested for these markers. All of the cases were negative for MOC-31, Ber-EP4, CEA, CD15, TAG-72, TTF-1, chromogranin A, synaptophysin, CD99, and desmin. The mean survival of the six patients for whom this information was available was 8.2 months. It is important for pathologists to be aware that mesotheliomas can present small cell features and, because of this, they can be confused with other malignancies that can exhibit similar morphology. The value of immunohistochemistry in the differential diagnosis of these tumors is discussed.

In plain English

This article was a case series by a pathologist at the University of Texas MD Anderson Cancer Center. It described eight cases of mesothelioma with small cell features, a rare form whose existence some investigators had questioned. The cases were found by reviewing 960 mesothelioma cases in the department's files, which is 0.8%. Seven patients were men and one was a woman, aged 52 to 74. All tumors arose in the pleura. Four patients had a history of asbestos exposure and three a history of smoking. The article did not describe the type or amount of asbestos exposure. Four tumors were epithelioid and four biphasic. Small cells made up 80 to 100% of the tumor in the four biopsy samples and 15 to 20% in the four pneumonectomy specimens. The small cells stained for calretinin in every case. None of the cases tested were positive for markers such as TTF-1, CEA, synaptophysin, CD99 or desmin. All six patients with follow-up information died of disease 3 to 17 months after diagnosis (mean 8.2 months). The author concluded that pathologists should be aware that these mesotheliomas can be confused with other small cell tumors.

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 series (report of eight cases) with light microscopy, immunohistochemistry and, in three cases, electron microscopy
• Who was studied: Eight patients with pleural mesothelioma with small cell features (seven men, one woman, aged 52 to 74, mean 64.8), identified from 960 mesothelioma cases in the files of the Department of Pathology, University of Texas MD Anderson Cancer Center; dates not given
• Exposure: History of asbestos exposure in four of the eight patients (fiber type, product, job and dose not reported); smoking history in three
• Main results:
  • 8 of the 960 mesothelioma cases reviewed (0.8%) were mesotheliomas with small cell features
  • All eight mesotheliomas originated in the pleura
  • Four tumors were epithelioid and four were biphasic
  • Small cells made up 80 to 100% of the tumor in the biopsy material (cases 1, 6, 7 and 8) and 15 to 20% in the pneumonectomy specimens (cases 2, 3, 4 and 5)
  • Mitotic activity was generally low, fewer than 5 mitoses per 10 high-power fields, except in case 1, which had about 20 per 10 high-power fields
  • In all cases the small cells reacted strongly for calretinin. They reacted strongly for pan-keratin and keratin 7 in all cases stained for these. All cases tested for keratin 5/6, WT1, podoplanin and mesothelin were positive, with variable staining.
  • None of the cases stained for MOC-31, Ber-EP4, CEA, CD15, TAG-72, TTF-1, chromogranin A, synaptophysin, CD99 or desmin were positive
  • All six patients with follow-up information died of disease 3 to 17 months after diagnosis (mean 8.2 months); follow-up was not available for two
• The authors' conclusion: The author concluded that mesotheliomas with small cell features are rare but that pathologists should be aware of them because they can be confused with other tumors with small cell morphology. The author also concluded that immunohistochemistry can help with the diagnosis, and that these tumors should be considered a poorly differentiated variant of epithelioid mesothelioma.
• Limitations the authors state:
  • The tissue sent for electron microscopy contained only the non-small cell part of the tumors, so the small cells were not studied by electron microscopy
  • Treatment information was not available for two patients

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, Epithelioid, Pleura, Asbestos Exposure, Biphasic Mesothelioma, Biopsy, Pneumonectomy, Calretinin.

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