A Case of Duodenal Metastasis From Malignant Pleural Mesothelioma Diagnosed by Gastrointestinal Endoscopy Following Progressive Anemia During Salvage Chemotherapy.

Malignant pleural mesothelioma (MPM) primarily progresses through direct invasion into the lung and pleura and is a refractory tumor in which asbestos exposure is a major underlying factor in most cases. Hematogenous metastasis of MPM is not uncommon in advanced stages, and reports suggest that metastatic sites may impact prognosis. Gastrointestinal metastases, ranging from the stomach to the colon, have been sporadically observed, but metastases to the small intestine and duodenum are exceedingly rare. Here, we report a case in which duodenal metastasis of MPM was endoscopically identified during the patient's lifetime while undergoing salvage chemotherapy following treatment with an immune checkpoint inhibitor and cytotoxic chemotherapy. Given the rarity and clinical significance of such cases, we present this report with a review of the relevant literature.