Peritoneal Well-Differentiated Papillary Mesothelial Tumor (WDPMT): Case Report and Literature Review

The pathogenesis and biological behavior of well-differentiated papillary mesothelial tumors (WDPMT) are poorly understood. WDPMT can arise in both the pleura and the peritoneum. As its benign and malignant features are often ambiguous, establishing an optimal treatment strategy can be challenging. In this report on peritoneal WDPMT, we analyzed nine Japanese cases, including our own case involving a 70-year-old male, and eight additional cases identified through a literature review from 2002 to 2025. The patients’ ages (median; range) were 47 years (range, 30 - 71 years), and 6 of the 9 patients were female. Almost all cases were incidentally detected and presented as multiple raised lesions on the abdominal peritoneum associated with ascites in six cases. Pathologically, the lesions retained BAP1expression and were considered unrelated to asbestos exposure. Treatment was variable: chemotherapy in 2, observation in 5, and no information in 2. All nine patients were alive at the time of reporting, with a median follow-up period of 8 months (range, 6 - 84 months). One case of late recurrence was reported in these cases.