Primary diffuse malignant epithelioid peritoneal mesothelioma of the greater omentum in an asbestos-naive patient: a case report

Background Malignant mesothelioma is a rare malignant neoplasm of mesothelial origin, with primary involvement of the greater omentum being exceptionally uncommon. Nonspecific clinical manifestations often lead to misdiagnosis, and cases without asbestos exposure further increase diagnostic complexity. Case presentation A 71-year-old male without asbestos exposure was admitted for recurrent diarrhea (>1 year), abdominal distension (>10 days), and unintentional weight loss (5 kg in 3 months). Physical examination revealed a 20-cm firm abdominal mass, and abdominal contrast-enhanced CT showed omental-peritoneal “cake-like” thickening with massive peritoneal effusion. Laparoscopic palliative tumor resection and peritoneal effusion drainage were performed, and postoperative pathology/immunohistochemistry (CK+, CR+, CK5/6+, D2-40+, WT1+ , CD20-, CDX2-) confirmed epithelioid mesothelioma of the omentum. Postoperative management included anti-infective therapy, nutritional support, and Cinobufacini Capsule-based anti-tumor treatment, with stable disease control at 3-month follow-up. Conclusion Definitive diagnosis of primary greater omental malignant mesothelioma relies on pathology and immunohistochemistry. For unresectable cases, palliative surgery combined with individualized adjuvant therapy may achieve favorable short-term outcomes, highlighting the need for early clinical suspicion in patients with unexplained abdominal symptoms.