A 69-year-old man was diagnosed as having diffuse large B-cell lymphoma (DLBCL) of the thyroid. Complete remission with chemotherapy was observed for 5 years without relapse. Ten years after the initial diagnosis, he visited our hospital with a complaint of abdominal pain, and abdominal computed tomography revealed a mass measuring 48 mm in diameter in the mesentery around the terminal ileum. After admission, the mass enlarged rapidly, and the patient developed bloody stool. Colonoscopy revealed a submucosal tumor-like lesion and an ulcer in the terminal ileum. Hemostasis was difficult both endoscopically and angiographically; therefore, we performed ileocecal resection, and DLBCL was diagnosed from the resected tissue specimen. In this patient, DLBCL was identified because of gastrointestinal bleeding. Rapid progression is possible with malignant lymphoma of the gastrointestinal tract, as in our patient; therefore, these tumors should be followed carefully.
