Primary Extramedullary Plasmacytoma in the Gastroduodenal Canal Associated With Epstein-Barr Virus-Associated Adenocarcinoma of the Stomach: A Case Report.

The coexistent occurrence of a lymphoid neoplasm with adenocarcinoma of the stomach is rare. We report herein a case of gastroduodenal extramedullary plasmacytoma simultaneously complicated by multiple gastric Epstein-Barr virus (EBV)-associated adenocarcinomas. The patient underwent distal gastrectomy to treat an adenocarcinoma occupying the gastric antrum. Histopathological examination revealed a massive submucosal plasma cell proliferation adjacent to the adenocarcinoma involving the pylorus to the duodenal bulb. Lambda immunoglobulin light chain restriction indicated that these plasma cells were monoclonal. Because the clinical investigation revealed no other lymphoid neoplasms, primary extramedullary plasmacytoma of the stomach was diagnosed. The histological examination of the resected stomach revealed 3 additional adenocarcinomas invading from the mucosa to the submucosa. A thorough histological examination of the remnant stomach resected 2 weeks after the first surgery revealed 2 additional adenocarcinomas in the remnant specimen, yielding a total of 6 carcinomas, all of which represented EBV-associated gastric carcinomas (EBV-GC). This is the second case report of gastric plasmacytoma concurrent with adenocarcinoma. Moreover, the plasmacytoma showed a conspicuous morphologic feature resembling Mott cells. Because Helicobacter pylori (HP) infection was also elucidated, this rare case may indicate a role of EBV or HP in carcinogenesis of both adenocarcinoma and lymphoplasmacytic neoplasms.