A 60-year-old man, who visited our hospital for further examination of atrophic gastritis on gastric roentgenography and positive of fecal occult blood test on physical examination. Esophagogastroduodenoscopy revealed open-type atrophic gastritis and Helicobacter pylori was positive on urea breath test. Therefore, eradication therapy was performed and successfully eradicated for H.pylori infection. Colonoscopy revealed a submucosal tumor-like elevated lesion in the rectosigmoid colon. The histopathological findings showed chronic inflammation with severe lymphocyte infiltration. After three years and one month, the histopathological findings revealed mucosa-associated lymphoid tissue lymphoma; however, accumulation rate was higher than that on the previous fluorodeoxyglucose-positron emission tomography; hence, we recommended surgery. Laparoscopic partial rectosigmoidectomy was performed, and the diagnosis was diffuse large B-cell lymphoma with lymph node metastasis. Hence, chemotherapy with 3 courses of rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone, was administered. The patient is being followed up.
