Malignant pleural effusion is a frequent situation in pulmonary medicine. However, it is sometimes difficult to recognize the underlying etiology. The aim of this review is to provide the key characteristics of primary and metastatic pleural neoplasms.

A review of the recent literature regarding pleural neoplasia is provided.

Malignant pleural mesothelioma (MPM) is the commonest primary pleural epithelial tumor showing remarkable histological heterogeneity often with prognostic significance. Various genetic alterations like changes in INK4 locus, NF2, BAP1 but also epigenetic changes are present in MPM. It should be distinguished from atypical mesothelial hyperplasia, mainly through morphological and clinical criteria, and from other rare primary and metastatic tumors, for which immunohistochemistry is rather important. Solitary fibrous tumor, the commonest primary pleural mesenchymal tumor is characterized by STAT6 overexpression. Other primary tumors, like adenomatoid tumor, well-differentiated papillary mesothelioma, synovial sarcoma, vascular tumors, various other sarcomas, thymic tumors and tumors of uncertain histogenesis are rarely encountered in the pleura. In contrast, metastatic disease is the commonest neoplasia of the pleura, and especially lung, breast and lymphoid malignancies.

The basic pathological, immunohistochemical and molecular characteristics of these entities are provided in the current review, along with their differential diagnosis.