J Pathol Transl Med.  2020 Nov;54(6):497-503. 10.4132/jptm.2020.09.14.

Can BAP1 expression loss in mesothelial cells be an indicator of malignancy?

• Ozdemir HG
• Kokten SC
• Barisik NO

• KMID: 2509503
• DOI: http://doi.org/10.4132/jptm.2020.09.14

Abstract

Background
Malignant mesothelioma is a highly aggressive tumor that can be confused with a benign mesothelial lesion, especially cytomorphologic lesions. BRCA1-associated protein 1 (BAP1) acts as a tumor suppressor. In this study, we aim to investigate the value of BAP1 staining of malignant mesothelioma cases with expression loss and diagnosis in cell block and biopsy tissue.
Methods
Between January 2009 and March 2017, 64 mesotheliomas, 117 reactive mesothelial hyperplasias, and 20 fibrinous pleuritis/pericarditis were diagnosed with morphologic and immunohistochemical findings in our pathology clinic and were included in the study. Formalin-fixed, paraffin-embedded tissues were immunohistochemically examined for BAP1. Inflammatory and stromal cells were used as positive internal controls. BAP1 was assessed for nuclear staining in mesothelial cells.
Results
Examinations of the relationship between patient diagnosis and BAP1 biopsy status showed that the BAP1 loss rate (76.6%) was significantly higher in malignant mesothelioma cases than in other benign diseases (0%) (p<.001). Sensitivity and specificity were 76.56% and 100%, respectively, for biopsy tissue from malignant mesothelioma. Sensitivity and specificity were both 100% for BAP1 test on cell block tissue. Furthermore, the consistency between BAP1 cell block and biopsy results was excellent (ĸ=0.90) and the correlation was significant (p<.001).
Conclusions
This study shows that BAP1 expression loss in both cytology and biopsy tissue in biopsy-confirmed malignant mesothelioma cases is an essential parameter for malignant mesothelioma diagnosis.

Keyword

Asbestosis; BAP1; Immunohistochemistry; Malignant mesothelioma; Pleura

Figure

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  Fig. 1. BRCA1-associated protein 1 (BAP1) immunohistochemistry results in reactive mesothelial hyperplasia. Biopsy material with hematoxylin and eosin staining (A) and BAP1 immunohistochemistry (B) with strong nuclear staining. Cell block material with BAP1 immunohistochemistry staining. (C) Note the strong nuclear and weak nonspecific cytoplasmic staining. (D) An example of a fibrinous pleuritis case with BAP1 staining.

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  Fig. 2. BRCA1-associated protein 1 (BAP1) immunohistochemistry results in malignant mesothelioma. Biopsy material with hematoxylin and eosin staining (A) and loss of BAP1 expression (B) with inflammatory cells as a positive internal control in epithelioid mesothelioma. Cell block material with BAP1 staining (C). BAP1 normal expression in sarcomatoid mesothelioma (D).

Reference

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