Epithelioid and sarcomatoid malignant pleural mesothelioma in endoscopic gastric biopsies: a diagnostic pitfall

Pleural malignant mesothelioma (MM) usually presents with chest pain, pleural effusion, or cough in middle-aged and elderly individuals with a history of asbestos exposure, but may rarely present at unusual metastatic sites. The luminal gastrointestinal (GI) tract is only rarely involved in patients with wide-spread disease at autopsy. Encountering MM in endoscopic GI biopsies is an exceptionally rare event in surgical pathology practice and may therefore pose great diagnostic challenges if not considered, in particular if the clinical history is not informative or the GI symptoms are the presenting signs of the disease. To our knowledge, only three cases of epithelioid mesothelioma (EM) involving the luminal GI tract (intestine) have been reported so far, but no case of sarcomatoid MM (SM) involving the GI mucosa has been described. We herein present the first two cases of MM (one each of EM and SM) of the pleura, presenting in endoscopic gastric biopsies as small polypoid lesions and poorly healing ulcers 30 and 35 months after the initial diagnosis of pleural MM, respectively. The major differential diagnoses encompass primary or metastatic adenocarcinoma in case one and cytokeratin-positive (KIT negative!) GI stromal tumors (GISTs) and sarcomatoid carcinoma in case two, as well as other rare entities.