Cytopathology of malignant mesothelioma of the pleura in fine-needle aspiration biopsy

The cytologic findings in fine-needle aspiration biopsy (FNAB) of 9 histolo gically immunohistochemically, and ultrastructurally confirmed malignant me sotheliomas of the pleura were reviewed. There were 4 epithelial malignant mesotheliomas (EMM), 3 sarcomatous mesotheliomas (SM), I mixed malignant me sothelioma (MMM), and 1 poorly differentiated malignant mesothelioma (PDMM) . In FNAB, three EMMs yielded polygonal malignant cells with oval nuclei an d prominent nucleoli, singly, in small sheets, and in tridimensional cluste rs with smooth or lobulated contours. In one EMM, only atypical mesothelial cells with pr-eminent nucleoli were seen singly and in loose aggregates. I n FNAB, two SM showed malignant spindle-shaped cells (MSC) with scant, ill- defined cytoplasm singly and in loose aggregates. Cohesive clusters of elon gated and polygonal cells with ill-defined, clear cytoplasm and pleomorphic nuclei containing small or prominent nucleoli were observed in one SM, wit h extensive clear-cell changes, In needle aspirates, the MMM showed polygon al malignant cells in clusters admixed with MSC. The PDMM displayed single and clustered large pleomorphic malignant cells, with prominent single or m ultiple nucleoli. Electron microscopic examination of minute tissue fragmen ts retrieved from the FNAB in 2 cases of EMM revealed epithelial mesothelia l cells with well-formed desmosomes and long slender microvilli (LSM) on th e free tumor cell surfaces. In one case, LSM in direct contact with collage n fiber bundles in the tumor tissue matrix were observed supporting the dia gnosis of an invasive EMM. (C) 1999 Wiley-Liss, Inc.