Diffuse pleural mesothelioma with epithelioid and angiosarcomatous components - a hitherto undescribed pattern of differentiation

Frequent expression of conventional endothelial markers in pleural mesothelioma: usefulness of claudin-5 as well as combined traditional markers to distinguish mesothelioma from angiosarcoma

OBJECTIVES

Distinguishing pleural sarcomatoid mesotheliomas from true sarcomas is challenging because the former does not always express the mesothelial markers, and diagnosis is often made on the basis of keratin expression. Consequently, sarcomas such as angiosarcomas that express keratin complicate the differential diagnosis. Furthermore, some mesotheliomas have been reported to express endothelial markers. The aim of this study is to identify useful markers for distinguishing pleural sarcomatoid mesothelioma from angiosarcoma.

MATERIALS AND METHODS

This study enrolled 147 patients with pleural mesothelioma-93 with epithelioid, 25 with biphasic, and 29 with sarcomatoid subtypes-and 41 patients with angiosarcomas in various organs. The expression levels of cytokeratin, mesothelial, and endothelial markers were assayed in both groups to identify the markers that could assist in distinguishing mesothelioma from angiosarcoma. Cytokeratin (AE1/AE3, CAM 5.2), endothelial (CD31, CD34, ERG, factor VIII, and claudin-5), and mesothelial (calretinin, WT-1, podoplanin (D2-40), EMA, and CK5/6) markers were immunohistochemically assayed using tissue blocks.

RESULTS

More than 90% of the mesotheliomas and less than 20% of the angiosarcomas expressed cytokeratin. Calretinin was expressed in 82% of all types of mesotheliomas but in only 48% of sarcomatoid mesotheliomas. Endothelial markers were expressed in mesothelioma tissues-CD31 in 10.3%, CD34 in 3.5%, ERG in 29%, and factor VIII in 3.4%-and the positivity was higher in sarcomatoid than in epithelioid and biphasic mesotheliomas. Claudin-5 was expressed in all the angiosarcomas, but not in any of the mesotheliomas.

CONCLUSION

We found overlapping immunophenotypes in pleural mesotheliomas and angiosarcomas, but the sensitivity and specificity of claudin-5 expression were sufficient to distinguish between them. The differential diagnosis of mesothelioma should therefore include claudin-5 in a panel of immunohistochemical markers to distinguish mesothelioma from angiosarcoma.

Guidelines for Pathologic Diagnosis of Malignant Mesothelioma 2017 Update of the Consensus Statement From the International Mesothelioma Interest Group

CONTEXT

- Malignant mesothelioma (MM) is an uncommon tumor that can be difficult to diagnose.

OBJECTIVE

- To provide updated, practical guidelines for the pathologic diagnosis of MM.

DATA SOURCES

- Pathologists involved in the International Mesothelioma Interest Group and others with an interest and expertise in the field contributed to this update. Reference material included up-to-date, peer-reviewed publications and textbooks.

CONCLUSIONS

- There was discussion and consensus opinion regarding guidelines for (1) distinguishing benign from malignant mesothelial proliferations (both epithelioid and spindle cell lesions), (2) cytologic diagnosis of MM, (3) recognition of the key histologic features of pleural and peritoneal MM, (4) use of histochemical and immunohistochemical stains in the diagnosis and differential diagnosis of MM, (5) differentiating epithelioid MM from various carcinomas (lung, breast, ovarian, and colonic adenocarcinomas, and squamous cell and renal cell carcinomas), (6) diagnosis of sarcomatoid MM, (7) use of molecular markers in the diagnosis of MM, (8) electron microscopy in the diagnosis of MM, and (9) some caveats and pitfalls in the diagnosis of MM. Immunohistochemical panels are integral to the diagnosis of MM, but the exact makeup of panels employed is dependent on the differential diagnosis and on the antibodies available in a given laboratory. Depending on the morphology, immunohistochemical panels should contain both positive and negative markers for mesothelial differentiation and for lesions considered in the differential diagnosis. Immunohistochemical markers should have either sensitivity or specificity greater than 80% for the lesions in question. Interpretation of positivity generally should take into account the localization of the stain (eg, nuclear versus cytoplasmic) and the percentage of cells staining (>10% is suggested for cytoplasmic and membranous markers). Selected molecular markers are now being used to distinguish benign from malignant mesothelial proliferations. These guidelines are meant to be a practical diagnostic reference for the pathologist; however, some new pathologic predictors of prognosis and response to therapy are also included.

Vasculogenic mimicry in malignant mesothelioma: an experimental and immunohistochemical analysis

Vasculogenic mimicry, the process in which cancer cells form angiomatoid structures independent of or in addition to host angiogenesis has been recorded in several otherwise non-endothelial malignant neoplasms. This study describes evidence of routine vascular mimicry by human mesothelioma cell lines in vitro, when the cell lines are cultured alone or co-cultured with human umbilical vascular endothelial cells, with the formation of angiomatoid tubular networks. Vasculogenic mimicry is also supported by immunohistochemical demonstration of human-specific anti-mitochondria antibody labelling of tumour-associated vasculature of human mesothelioma cells xenotransplanted into nude mice, and by evidence of vascular mimicry in some biopsy samples of human malignant mesotheliomas. These studies show mosaic interlacing of cells that co-label or label individually for immunohistochemical markers of endothelial and mesothelial differentiation. If vascular mimicry in mesothelioma can be characterised more fully, this may facilitate identification of more specific and targeted therapeutic approaches such as anti-angiogenesis in combination with chemotherapy and immunotherapy or other therapeutic approaches.

Guidelines for pathologic diagnosis of malignant mesothelioma: 2012 update of the consensus statement from the International Mesothelioma Interest Group

CONTEXT

Malignant mesothelioma (MM) is an uncommon tumor that can be difficult to diagnose.

OBJECTIVE

To provide updated practical guidelines for the pathologic diagnosis of MM.

DATA SOURCES

Pathologists involved in the International Mesothelioma Interest Group and others with an interest in the field contributed to this update. Reference material includes peer-reviewed publications and textbooks.

CONCLUSIONS

There was consensus opinion regarding (1) distinction of benign from malignant mesothelial proliferations (both epithelioid and spindle cell lesions), (2) cytologic diagnosis of MM, (3) key histologic features of pleural and peritoneal MM, (4) use of histochemical and immunohistochemical stains in the diagnosis and differential diagnosis of MM, (5) differentiation of epithelioid MM from various carcinomas (lung, breast, ovarian, and colonic adenocarcinomas, and squamous cell and renal cell carcinomas), (6) diagnosis of sarcomatoid mesothelioma, (7) use of molecular markers in the diagnosis of MM, (8) electron microscopy in the diagnosis of MM, and (9) some caveats and pitfalls in the diagnosis of MM. Immunohistochemical panels are integral to the diagnosis of MM, but the exact makeup of panels used is dependent on the differential diagnosis and on the antibodies available in a given laboratory. Immunohistochemical panels should contain both positive and negative markers. It is recommended that immunohistochemical markers have either sensitivity or specificity greater than 80% for the lesions in question. Interpretation of positivity generally should take into account the localization of the stain (eg, nuclear versus cytoplasmic) and the percentage of cells staining (>10% is suggested for cytoplasmic membranous markers). These guidelines are meant to be a practical reference for the pathologist.