Pleural malignant mesothelioma with osteoclast-like giant cells

Reported herein is the first case of malignant mesothelioma with osteoclast-like giant cells (OGC) in a 55-year-old man, a building contractor. Open thoracoscopic biopsy from the left parietal pleura showed a pleomorphic tumor composed of round to spindle cells mixed with numerous OGC; focal hemorrhage and necrosis were observed, but neither bone nor osteoid tissue was seen. The tumor cells had eosinophilic cytoplasm and round to oval nuclei with varying degrees of atypia. OGC had multiple small uniform nuclei without atypia and large eosinophilic cytoplasm, similar to giant cells of the so-called giant-cell tumors. On immunohistochemistry the tumor cells stained positive for AE1/AE3 and mesothelial markers, including calretinin, thrombomodulin, D2-40, and negative for carcinoma markers, including CEA, MOC31, and thyroid transcription factor-1. Consequently the tumor was diagnosed as malignant mesothelioma with OGC. Because malignant mesothelioma with OGC has not been reported to date, described herein are the histopathology and immunohistochemistry findings of this tumor, and a review of the literature.