Collision of EBV-associated gastric carcinoma and primary gastric extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue in the remnant stomach.

Reported herein is a case of EBV-associated gastric carcinoma with primary gastric extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma). A 69-year-old Japanese man was found to have an ulcer lesion in his stomach on endoscopy, and a biopsy indicated malignancy. He underwent gastrectomy. Microscopically the tumor had features typical of lymphoepithelioma-like carcinoma. The neoplastic epithelial cells proliferated in a trabecular fashion. On in situ hybridization for EBV-encoded RNA, positive signals were observed in most neoplastic epithelial cells. Numerous lymphocytes surrounded the neoplastic epithelial cells. In the stroma, numerous lymphocytes with mild atypia were positive for CD20 and CD79a. In addition, monoclonal proliferation of B cells was confirmed on polymerase chain reaction for IgH. These findings supported MALT lymphoma. The coexistence of EBV-associated gastric carcinoma and MALT lymphoma is extremely rare.