Macroscopy: "Right pleura biopsy". A fragment of soft, tan tissue bearing 1 soft, nodular surface, the other surface is shiny with attached ragged fatty tissue 30 x 22 mm, 8 mm thick. Fatty surface inked blue.
Microscopy: The sections show fragments of skeletal muscle and fibroadipose connective tissue lined by mesothelium. The mesothelium is thrown into exuberant folds and pseudo-papillary structures about underlying myxoid and chronically inflamed stroma. The cells have enlarged nuclei with irregular nuclear membranes, vacuolated chromatin and prominent round nucleoli. Scattered mitoses are identified. The cells, arranged in variably sized glandular and cribriform structures and solid nests, appear to infiltrate the underlying connective tissues, including fat.
Immunohistochemistry: The atypical cell population immunoreacts with antibodies against CK5/6, podoplanin, HBME1, calretinin and WT1 and is negative with CK7, CK20, TTF1 and TAG-72.
Conclusion: Malignant mesothelioma.