Malignant mesothelioma is an aggressive cancer associated with asbestos exposure with median survival time of 8 to 14 months following diagnosis. Given that mesothelial cells also line the peritoneum and pericardium, malignant mesothelioma can present in unusual sites and in patients with nonrespiratory complaints. A 73-year-old male presented to the emergency department for worsening intermittent diffuse abdominal pain for the past 3 months with associated unintentional 40-pound weight loss, early satiety, and diarrhea. He denied exposure to asbestos. Computed tomography imaging revealed multiple masses concerning for malignancy including the primary retroperitoneal mass, a mass involving the terminal ileum, and a mass in the right upper lung. Esophagogastroduodenoscopy demonstrated significant mass effect within the stomach without signs of endoluminal infiltration. Computed tomography–guided biopsy of the retroperitoneal abdominal and intramuscular paraspinal masses was performed. Stage IV epithelioid mesothelioma was confirmed when hematoxylin and eosin staining revealed pleomorphic malignancy nuclei containing a vesicular chromatin pattern and prominent nucleoli and immunohistochemical staining was positive for CK Oscar, cytokeratin 7, GATA3, calretinin, EMA, and CK5/6. He was started on cisplatin, pemetrexed, and bevacizumab but developed severe abdominal pain with pneumoperitoneum and bowel perforation 1 month later and expired shortly thereafter. To our knowledge, this represents a highly atypical presentation of malignant mesothelioma considering the involvement of the retroperitoneum with diffuse lesions in the abdominopelvic cavity and thorax (sparing the lung pleurae). This case also calls attention to the occurrence of malignant mesothelioma in patients without known asbestos exposure and the crucial role of pathology in diagnosing atypical presentations.
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