Well-differentiated papillary mesothelioma with invasion to the chest wall.

Well-differentiated papillary mesothelioma (WDPM) is an uncommon tumor with a papillary architecture, bland cytologic features, a tendency toward superficial spread without invasion, and good prognosis with prolonged survival. WDPM occurs primarily in the peritoneum of women, but also rarely in the pleura. We here report a case of 48-year-old woman who developed WDPM in the pleura with no history of asbestos exposure. Tumors were multifocal and widespread with a velvety appearance on the surface of parietal and visceral pleurae resected by extrapleural pneumonectomy (EPP). Tumors showed papillary structures with fibrovascular cores and lined by epithelioid cells. Immunohistochemically, these epithelioid tumor cells were positive for epithelial membrane antigen (EMA), a marker of malignant mesothelioma, with more than 50% positive for p53. Tumor cells microinvaded into subpleural parenchyma of the lung and minimally spread to adipose tissues of the mediastinal lesion. In addition, tumor cells invaded into the chest wall with a trabecular or glandular architecture. Based on these findings, this case is pathologically considered as WDPM of the pleura with malignant potential.