Interobserver variation in the assessment of the sarcomatoid and transitional components in biphasic mesotheliomas

Our plain-English summary of Interobserver variation in the assessment of the sarcomatoid and transitional components in biphasic mesotheliomas, by S. Dacic, N. Le Stang, A. Husain, et al (Modern Pathology, 2020).

The study

• Authors: S. Dacic, N. Le Stang, A. Husain, B. Weynand, M.B. Beasley, K. Butnor, D. Chapel, A. Gibbs, S. Klebe, S. Lantuejoul, A.C. Roden, V. Roggli, H. Tazelaar, J.M. Vignaud, F. Galateau-Sallé
• Journal: Modern Pathology
• Published: 2020;33(2):255-262
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The percentage of sarcomatoid component has an impact on prognosis in patients with biphasic malignant pleural mesothelioma. Recent study showed that the transitional pattern similar to sarcomatoid component of malignant mesothelioma has negative prognostic significance. Practice guidelines recommend quantification of sarcomatoid component despite poor diagnostic reproducibility of biphasic mesothelioma among thoracic pathologists. The aim of this study was to determine the interobserver agreement in the quantification of sarcomatoid component, and in the diagnosis of a transitional component in the biphasic malignant mesothelioma. Thirteen experts in thoracic pathology reviewed the representative H&E and cytokeratin whole-slide images of the 54 biphasic mesotheliomas, without knowledge of BAP1 or p16 deletion status, and completed the survey of 25 questions. The overall interobserver agreement in the assessment of the percentage of the sarcomatoid component in 25% increments was good (wK = 0.62). Excellent agreement was present in 14 of 54 cases (26%), and 3 cases were unanimously scored. Excellent agreement was reached for the cases with 0-24% and > 75% of the sarcomatoid component.The most commonly used criteria for the diagnosis of sarcomatoid component were malignant spindle cells, frank sarcomatoid features and high N/C ratio. The overall interobserver agreement for transitional pattern was fair (wK = 0.40). Unanimous opinion about the absence of transitional pattern was observed in only one case. At least 70% agreement regarding the presence of transitional pattern was observed in 12 cases, with the rest of the cases showing a wide range of disagreement. Morphologic characteristics that favor transitional pattern over non-transitional include sheet-like growth of cohesive, plump, elongated epithelioid cells with well-defined cell borders and a tendency to transition into spindle cells. Our study defined precise morphologic criteria that may be used in the differential diagnosis between transitional pattern and other mesothelioma subtypes including sarcomatoid and epithelioid.

In plain English

This study measured how consistently expert pathologists read biphasic mesothelioma tissue. It did not study asbestos exposure. Thirteen members of the International Mesothelioma Panel reviewed slides from 54 randomly selected, surgically removed biphasic mesotheliomas (tumors with both epithelioid and sarcomatoid tissue) using a 25-question survey, though one reviewed only 12 cases and partially completed the survey. Agreement was scored with weighted kappa. When the pathologists estimated the share of sarcomatoid tissue in 25% bands, overall agreement was rated good (weighted kappa 0.62). Agreement was excellent in 14 of 54 cases (26%). It was excellent for cases with 0–24% or more than 75% sarcomatoid tissue and less consistent for cases in between. Agreement on whether a 'transitional' pattern was present was fair (weighted kappa 0.40). At least 70% of reviewers agreed it was present in 12 cases. The authors concluded that more education among pathologists is needed to improve reproducibility. They noted several limits: reviewers saw only one or two slides per case, all reviewers were experts, the cases had already been diagnosed as biphasic, and only large surgical specimens were included.

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: Interobserver agreement study: 13 expert pathologists reviewed the same cases and completed a 25-question survey
• Who was studied: 54 surgically resected biphasic mesotheliomas, randomly selected from the case files of the MESOPATH center (10 cases) and two co-authors (34 and 10 cases); no dates given. One of the 13 panelists reviewed only 12 cases.
• Exposure: Not studied: this was a study of agreement between pathologists reading tumor slides; no asbestos or other exposure was assessed
• Main results:
  • One of the 13 panelists reviewed only 12 of the 54 cases and completed the survey only partially
  • Overall agreement among the pathologists on the percentage of sarcomatoid component, scored in 25% increments, was good (weighted kappa 0.62)
  • For the sarcomatoid percentage, agreement between pathologists ranged from poor (kappa 0.14) to excellent (kappa 1.0)
  • Excellent agreement on sarcomatoid percentage was reached in 14 of 54 cases (26%), and 3 cases were scored unanimously
  • Excellent agreement was reached for cases with 0–24% and more than 75% sarcomatoid component
  • There was less consensus for cases estimated to have 25–49% and 50–74% sarcomatoid component
  • The most commonly used criteria for diagnosing the sarcomatoid component were malignant spindle cells, frank sarcomatoid features and high nuclear-to-cytoplasmic (N/C) ratio
  • The MESOPATH pathologists determined that a transitional pattern was present in 42 of the biphasic mesotheliomas
  • Overall agreement among the panel on the transitional pattern was fair (weighted kappa 0.40), ranging from poor (0.07) to excellent (1.0)
  • All panelists agreed that a transitional pattern was absent in only one case
  • At least 70% agreement that a transitional pattern was present occurred in 12 cases; the remaining cases showed a wide range of disagreement
  • Features that led panelists to favor a transitional pattern were sheet-like growth of cohesive, plump, elongated epithelial cells with a tendency to transition into spindle cells
• The authors' conclusion: The authors concluded that more education among pathologists is needed to improve their reproducibility in diagnosing the transitional pattern
• Limitations the authors state:
  • Only one or two representative slides per case were reviewed, whereas many sections are available in daily practice
  • The reviewers were experienced experts, which may not reflect general practicing pathologists
  • All cases had already been unequivocally diagnosed as biphasic by MESOPATH and two other experts
  • Only large surgical resection specimens were included, not smaller biopsies

Topics

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

Medical terms in this study, explained in our Lexicon: Sarcomatoid, Biphasic Mesothelioma, Prognosis, Pleural Mesothelioma, Malignant Mesothelioma, Pathology, BAP1, Spindle Cell.

Related studies

• The differential diagnosis between pleural sarcomatoid mesothelioma and spindle cell/pleomorphic (sarcomatoid) carcinomas of the lung: evidence-based guidelines from the International Mesothelioma Panel and the MESOPATH National Reference Center — A.M. Marchevsky, N. LeStang, et al. (2017)
• New Insights on Diagnostic Reproducibility of Biphasic Mesotheliomas: A Multi-Institutional Evaluation by the International Mesothelioma Panel From the MESOPATH Reference Center — F. Galateau Salle, N. Le Stang, et al. (2018)
• Biphasic malignant mesothelioma with epithelioid and sarcomatoid components (dedifferentiated mesothelioma) and intrapulmonary growth: a rare entity mimicking desquamative interstitial pneumonia — J. Laforga, A. Gonzalez Garcia (2020)
• Pleomorphic epithelioid diffuse malignant pleural mesothelioma: a clinicopathological review and conceptual proposal to reclassify as biphasic or sarcomatoid mesothelioma — K. Kadota, K. Suzuki, et al. (2011)
• GATA3 is a useful immunohistochemical marker for distinguishing sarcomatoid malignant mesothelioma from lung sarcomatoid carcinoma and organizing pleuritis — Z.H. Piao, X.C. Zhou, et al. (2021)
• Sarcomatoid Peritoneal Mesothelioma: Clinicopathologic Correlation of 13 Cases — E.N. Pavlisko, V.L. Roggli (2015)

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