Dual Immunotherapy for Pericardial Mesothelioma That Developed After a Decade‐Long Idiopathic Pericarditis: A Case Report

Malignant pericardial mesothelioma (MPeM) is exceptionally rare, and its association with long-standing idiopathic pericarditis remains unreported. We present a 46-year-old woman with a decade-long history of recurrent idiopathic pericarditis who developed multiple pericardial nodules, mediastinal lymphadenopathy, and metastatic liver and bone lesions. A core needle biopsy confirmed biphasic MPeM. Due to her pericardial condition, she initially received platinum-based chemotherapy instead of immunotherapy, but the disease progressed. She then underwent dual immune checkpoint inhibition (ICI) and achieved a significant clinical and radiological response. This case raises the possibility of chronic inflammation contributing to pericardial malignancy and underscores the potential role of dual ICI in this rare and challenging disease.