# Non-Asbestos-Related Malignant Peritoneal Mesothelioma: A Diagnostic Challenge in a Case of Unexplained Ascites

## TL;DR

This paper presents a rare case of peritoneal cancer without asbestos exposure, highlighting the difficulty in diagnosing it due to non-specific symptoms and the need for early histological testing.

## Contribution

The case emphasizes the diagnostic challenges of non-asbestos-related peritoneal mesothelioma and the importance of histological evaluation in unexplained ascites.

## Key findings

- The patient had epithelioid-type MPM confirmed by omental biopsy and BAP1 loss on immunohistochemistry.
- The patient was unsuitable for surgery or chemotherapy due to advanced disease and poor performance status.
- The case underscores the need for early histological evaluation in patients with unexplained recurrent ascites.

## Abstract

Malignant peritoneal mesothelioma (MPM) is a rare and aggressive malignancy arising from mesothelial cells of the peritoneum. It is most frequently linked to asbestos exposure, although up to half of cases occur without such history. Because of its vague and non-specific presentation, diagnosis is often delayed; cytology is frequently non-diagnostic, and histological confirmation with immunohistochemistry is required. Prognosis remains poor, although advances in cytoreductive surgery and intraperitoneal chemotherapy have improved outcomes in selected patients. We describe a man in his late 60s with no history of asbestos exposure who presented with progressive abdominal distension over 18 months. He underwent repeated paracenteses with negative cytology and multiple imaging studies, initially attributed to an intraductal papillary mucinous neoplasm (IPMN) under surveillance. Subsequent computed tomography (CT) demonstrated extensive peritoneal disease with omental caking and splenic lesions. Omental biopsy confirmed epithelioid-type MPM with BRCA1-associated protein 1 (BAP1) loss on immunohistochemistry. Given advanced disease and poor performance status, the patient was deemed unsuitable for surgery or chemotherapy and was managed with best supportive palliative care. This case highlights the diagnostic challenges of MPM, particularly in the absence of asbestos exposure and in the presence of coexistent pathology, and underscores the importance of early histological evaluation in patients with unexplained recurrent ascites.