83-year-old male, smoker who presented with dyspnea, cough, weight loss and chronic right sided pleural effusion.
Microscopic Description: Sections show fibrous plaques and fragments of necrosis. There are also nodular proliferations of lesional cells growing in sheets. The tumor cells are positive for pan-cytokeratin, cytokeratin 7, cytokeratin 5-6, cytokeratin 8-18, calretinin, and WT-1. The lesional cells are negative for cytokeratin 20, CD68, MOC31, TTF-1, p40, PAX 8, and Sox 10. A GMS stain is negative for fungal hyphae in block 1B. This immunophenotype is consistent with a mesothelial proliferation. Invasion into adjacent tissue is not identified.