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BAP1 Immunohistochemistry and p16 FISH in the Diagnosis of Malignant Peritoneal Mesothelioma
Poster

BAP1 Immunohistochemistry and p16 FISH in the Diagnosis of Malignant Peritoneal Mesothelioma

BAP1 Immunohistochemistry and p16 FISH in the Diagnosis of Malignant Peritoneal Mesothelioma
Poster

BAP1 Immunohistochemistry and p16 FISH in the Diagnosis of Malignant Peritoneal Mesothelioma

Objective: Peritoneal malignant mesothelioma (PMM) is an uncommon tumor, only 7-9% of all mesothelioma in Japan. Differential diagnosis between PMM and primary peritoneal serous carcinoma (PPSC), a high-grade serous carcinoma, may be difficult, and separating reactive mesothelial hyperplasia (RMH) from PMM can be even more challenging.


Methods: To help differentiate PMM from PPSC and RMH, we used immunohistochemistry to examine BAP1, and FISH to examine for homozygous deletion of 9p21. We used formalin-fixed, paraffin-embedded blocks from 22 PMMs (M:F=18:4; subtypes: 16 epithelioid, 6 biphasic), 11 PPSCs, and 10 RMHs.


Results: Seventeen of the mesotheliomas were classified as diffuse, while 5 were localized. Loss of BAP1 was seen in 10/21 (45%) of PMM, but all PPSC and all RMH were BAP1-positive. For the differentiation of PMM from PPSC and RMH of the peritoneum, the sensitivity and specificity for BAP1 in mesothelioma were 43% and 100%, respectively. FISH analysis revealed homozygous deletion of the 9p21 locus in 11/13 (85%) of PMM, but in none of RMH.


Conclusion: BAP1 loss is not a sensitive test, although specificity is very high for differentiating PMM from both PPSC and RMH. Homozygous deletion of 9p21 may be helpful for differentiating PMM from RMH.

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