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Mediastinal Extramedullary Plasmacytoma: a Surgical Case

━━ Background. Plasma cell neoplasms are classified as multiple myeloma and solitary plasmacytomas, the latter of which can be further classified into solitary plasmacytoma of the bone and extramedullary plasmacytoma. We herein report a rare resected case of extramedullary plasmacytoma of mediastinal origin. Case. An 82-year-old man was referred to our department because an anterior mediastinal nodule was confirmed via computed tomography (CT). CT showed a well-circumscribed tumor at the anterior mediastinum with no find-ings of mediastinal enlarged lymph nodes or pleura dissemination. Magnetic resonance imaging (MRI) showed no invasion into the surrounding tissue. Fluorodeoxyglucose positron emission tomography (FDG-PET) showed the abnormal accumulation of FDG in the tumor. We suspected that the patient had thymoma, and he underwent si-multaneous bilateral thoracoscopic extended thymectomy. A histopathological examination of the 4.0-cm-diameter tumor in the thymus showed invasion and proliferation of plasma cells with nuclear atypia. Immunohis-tochemical staining showed positivity for λ chain-CD138 and negativity for κ chain-CD20. We also found plasma cell invasion in the thymus outside the tumor, but invasion was not observed in the stump of the resected speci-men. Tumor metastasis was not observed in the superior mediastinal lymph node. The patient was diagnosed with mediastinal extramedullary plasmacytoma. After surgery, serum IgG- λ chain monoclonal protein was de-tected slightly via immunoelectrophoresis, but atypical cells were not clearly observed in the bone marrow. The patient is still alive without disease progression at 25 months post-operatively. Conclusion. We herein described a rare case of mediastinal extramedullary plasmacytoma. 2018;58:196-200)