Pleural Mesothelioma In Situ

**Semantic type:** Neoplastic Process

**Definition:** A preinvasive mesothelial neoplasm that arises on the surface of pleura and is characterized by the proliferation of mesothelial cells in a single layer without invasion into underlying tissues. It requires demonstration of nuclear BAP1 loss or cytoplasmic MTAP loss by immunohistochemistry, or CDKN2A homozygous deletion by FISH. It is a precursor lesion to malignant mesothelioma and usually occurs in older adults. Most patients have a history of asbestos exposure.

**Synonyms:** - PMIS - Pleural MesIS