[BRCA1 associated protein 1 (BAP1) expression in pleural diffuse malignant mesothelioma: A comparative cytological...

Diffuse malignant mesothelioma (MMD) is a rare disease. The diagnosis is difficult and needs an antibody panel. The tumor suppressor gene BRCA1 associated protein 1 (BAP1) is involved in several cancers, including MMD. Loss of BAP1 expression is correlated with BAP1 somatic or constitutional genetic defects. Our work assesses the value of integrating BAP1 in the panel of antibodies used for the diagnosis of MMD.

Immunohistochemical techniques were performed on cytological and histological specimens of MMD and adenocarcinoma pleural metastasis.

Of the 26 patients with MMD and the 24 patients with adenocarcinoma pleural metastasis, loss of BAP1 expression was observed in 11 (48%) and one adenocarcinoma (6%) on cytological specimens and in 12 MMD (48%) and in one adenocarcinoma (5%) on biopsy specimens. The concordance between immunocytochemistry and immunohistochemistry was 100%. The specificity of BAP1 was 100% on cytological and biopsy specimen for the diagnosis of malignancy in case of mesothelial proliferation.

Loss of BAP1 expression is an indicator of MMD in a context of mesothelial proliferation. This immunohistochemistry could be integrated in the panel of immunostaining used for MMD diagnosis, either on histological or cytological samples. Furthermore, loss of BAP1 expression guides the patient to an oncology genetic counseling in order to eliminate a MMD developed as part of a constitutional genetic defect.