A localized or multifocal mesothelioma arising from the peritoneum and less often the pleura. Cases arising from the peritoneum predominantly occur in women. It is characterized by the formation of papillae, covered by a single layer of blunt mesothelial cells. Mitotic figures are not present. There is no evidence of severe cytologic atypia. It has a relatively favorable clinical outcome, compared to malignant mesothelioma. The disease is Monarch Disease Ontology id MONDO_0003688 (well differentiated papillary mesothelioma). Also known as: WDPM, benign/Intermediate mesothelioma, well-differentiated mesothelial papillary neoplasm, well-differentiated mesothelial papillary tumor, well-differentiated mesothelial papillary tumour, well-differentiated papillary neoplasm of mesothelium, well-differentiated papillary neoplasm of the mesothelium, well-differentiated papillary tumor of mesothelium.