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Sisko Liisa Anttila

Malignant mesothelioma – update on pathology and IHC

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The incidence of malignant mesothelioma (MM) is still increasing in most countries. The histological diagnosis of MM may be challenging because MM has a wide spectrum of morphological presentations with partially different immunohistochemical characteristics. MM is divided into four main histological subtypes, i.e. epithelioid, sarcomatoid, desmoplastic and biphasic, and epithelioid and sarcomatoid subtypes each contain rare variants. With varying histology MM may resemble several other primary and secondary tumors occurring in the body cavities. The development of immunohistochemical markers has improved the diagnosis of epithelioid MM, but immunohistochemistry has only a minor role in the diagnosis of sarcomatoid and desmoplastic MM. For the diagnosis of epithelioid MM, a panel of antibodies is recommended, including positive and negative markers, the selection of markers depending on the tumor location in the pleural or peritoneal cavity, morphological features, possible previous malignant diseases, and clinical and imaging findings. It is recommended that each laboratory should optimize the antibody panel they use, and include only antibodies with at least 80 % sensitivity and specificity in the detection of epithelioid MM. Sarcomatoid and desmoplastic MM are in general negative for mesothelial markers, while a high proportion are positive for pancytokeratins. The knowledge of imaging and thoracoscopic findings of a patient is important, because the typical gross finding of diffuse MM may be the only feature separating a sarcomatoid carcinoma and sarcomatoid MM. Furthermore, diffuse epithelioid MM has to be distinguished from atypical mesothelial hyperplasia, and sarcomatoid (desmoplastic) MM from fibrosing pleuritis. Several antibodies and some molecular markers have been investigated as regards their capacity to separate benign and malignant mesothelial proliferations. So far, invasion of adjacent tissue is the only reliable marker of malignancy, but immunohistochemical markers, such as cytokeratins, may aid the demonstration of invasion.


Dr. Sisko Anttila, MD, PhD, is Head of the Jorvi Hospital Laboratory of Pathology at Helsinki University Hospital and HUSLAB, Espoo, Finland. Previously, between 1988 and 2007 (until 2014 part-time) she worked as chief physician and pathologist at the Finnish Institute of Occupational Health, Helsinki, Finland, and as visiting scientist at the University of California Los Angeles (1997-1998). She has published 111 original articles and several reviews concentrating on gene-environment interactions in pulmonary carcinogenesis. Her research group has discovered asbestos-specific molecular alterations in lung cancer, reported in several articles published 2006-2013. Dr. Anttila has special interest in pulmonary pathology, especially pathology of occupational lung diseases and malignant mesothelioma. She was a member of a working group establishing international criteria for asbestos-related diseases (Asbestos, Asbestosis, and Cancer, Helsinki Criteria for Diagnosis and Attribution 2014). She was editor and author for 3 chapters for a textbook of Occupational Cancers, published in 2014 by Springer.

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