Immunotherapy in Unresectable Epithelioid Peritoneal Mesothelioma

Background Peritoneal mesothelioma is a rare malignancy with limited treatment options. Immunotherapy has shown responses, particularly in patients with unresectable disease. Here we present an unresectable peritoneal mesothelioma with long-term response to immunotherapy. Case Presentation A 42-year-old woman with unresectable epithelioid peritoneal mesothelioma was treated with ipilimumab and nivolumab. She initially responded but developed grade 3 immune-mediated colitis. After clinical recovery, nivolumab monotherapy was successfully reintroduced with sustained disease control and no recurrence of colitis. Her disease continues to respond 22 months after initiation of immunotherapy. Conclusion This case highlights the potential role of immune checkpoint inhibitors (ICIs) in managing unresectable peritoneal mesothelioma and supports rechallenge with ICIs after immune-related adverse events, with close monitoring.