WHO Classification of Tumors of the Peritoneum, Pathology of the Peritoneum

The fifth edition of the World Health Organization classification of female genital tumors, tumors of the peritoneum chapter, contains two of the same categories as the fourth edition: the “mesothelial tumors” and the “epithelial tumors.” It has also added two new sections: “mesenchymal tumors specific to the peritoneum” and “tumor like lesions.” The former includes leiomyomatosis peritonealis disseminata (previously listed entity in its own category), abdominal fibromatosis, calcifying fibrous tumor, gastrointestinal stromal tumor, solitary fibrous tumor, endometrial stromal sarcoma (low and high grade), and desmoplastic round cell tumor (previously listed as a tumor of uncertain origin). The latter includes non-neoplastic entities, such as mesothelial hyperplasia, peritoneal inclusion cysts, transitional metaplasia, endosalpingiosis, histiocytic nodule, ectopic decidua, and splenosis. Lastly, the fifth edition has also added a “metastases to the peritoneum” category. In addition to...