β-catenin expression in benign and malignant pleural disorders.

Benign and malignant pleural processes display a large and overlapping spectrum of morphological appearances, and can be difficult to distinguish, histologically, from each other. β-catenin, a participant in the wingless-type (Wnt) transduction pathway, is involved in the pathogenesis of malignant mesothelioma and has received limited evaluation for its ability to serve as a diagnostic aid for distinguishing between individual pleural disorders. We performed immunohistochemistry for β-catenin on 10 pleural malignant mesotheliomas, 10 examples of mesothelial hyperplasia and 18 cases of organizing pleuritis. Although differences were noted in staining intensity between the mesothelioma and mesothelial hyperplasia groups, extensiveness and cellular location were similar. Staining intensity (mean +/- s.d.) in mesotheliomas (2.00 +/- 0.67) was significantly less intense than in mesothelial hyperplasia cases (3.00 +/- 0.00) (p=0.0005). Stromal cell staining was cytoplasmic in all cases, and endothelial cell staining was membranous, submembranous and cytoplasmic. Nuclear expression of β-catenin was not observed in any of the cases studied. This lack of nuclear staining in the stromal cells of organizing pleuritis differs markedly from the previously reported high frequencies of nuclear β-catenin expression in other pleural spindle cell proliferations (desmoid tumors and solitary fibrous tumors). In summary, the current study adds to previous work indicating a role for β-catenin in the genesis of pleural conditions including organizing pleuritis, mesothelial hyperplasia and malignant mesothelioma. Although IHC for β-catenin does not appear to be conclusive for separating benign from malignant mesothelial proliferations, it may be valuable for assisting in the differential diagnosis of mesothelial and spindle cell proliferations in the pleura.