Malignant peritoneal mesothelioma with lymph node metastasis that originated in the transverse colon

BACKGROUND: We report an extremely rare case of resection of localized biphasic malignant peritoneal mesothelioma of the transverse colon. CASE REPORT: Computed tomography and magnetic resonance imaging in a 72-year-old man showed a tumor with enhanced borders consistent with the transverse colon. Colonoscopy showed ulcerative lesions in the transverse colon, but histological examination showed no malignancy. A gastrointestinal stromal tumor was strongly suspected, so an extended right hemicolectomy was performed. Histopathological examination showed that the tumor was a localized malignant peritoneal mesothelioma of the transverse colon. The patient did not receive postoperative chemotherapy and died 18 months after surgery. CONCLUSIONS: The number of patients with malignant mesotheliomas is predicted to increase in the future both in Japan and in western countries. We report this case due to its probable usefulness in future studies pertaining to the diagnosis and treatment of malignant mesotheliomas.