A case of API2-MALT1-positive gastric MALT lymphoma with concomitant diffuse large B-cell lymphoma

API2-MALT1 translocation-positive gastric marginal zone lymphomas of mucosa-associated lymphoid tissue (MALT) lymphoma is thought to transform to diffuse large B-cell lymphoma (DLBCL) rarely. A 69-year-old man presented with epigastralgia. Esophagogastroduodenoscopy showed multiple ulcerations in the stomach. Endoscopic biopsies revealed MALT lymphoma, with Helicobacter pylori infection. The patient underwent eradication therapy with no improvement, and was thereafter followed without additional therapy at his request. Twelve years after initial diagnosis, follow-up computed tomography (CT) showed multiple nodules in bilateral lungs, and a needle biopsy revealed MALT lymphoma, the same as in the stomach and API2-MALT1 translocation was found. Because he again refused additional therapy, follow-up was continued. 15 years after initial diagnosis, CT showed lymphadenopathy at the splenic hilum. At first we suspected disease progression of gastric MALT lymphoma, however a needle biopsy revealed DLBCL without API2-MALT1. Thus, the tumor at the splenic hilum was finally diagnosed as a de novo DLBCL as a second malignancy. Although treatment with rituximab given his age and his wishes was attempted, he died of DLBCL 15 years after the initial diagnosis. We experienced an API2-MALT1-positive gastric MALT lymphoma with concomitant DLBCL, not transformed to DLBCL over a 15-year clinical course.