A 60-oyear-oold male visited a clinic because of gastric discomfort. This symptom was temporarily improved by a proton pump inhibitor, but it was worsened by discontinuation of the drug. He was referred to our hospital. Esophagogastroduodenoscopy showed an elevated lesion with multiple whitish small granular protrusions in the duodenal second portion, occupying two thirds of the circumference. The lesion was diagnosed to be a follicular lymphoma by histopathological examination including immunostaining of the biopsy specimens. He was admitted to our hospital. Abdominal CT scan showed no lymph node metastasis. Capsule endoscopy of the small intestine showed lymphoid follicles in the distal ileum in addition to the duodenal lesion. Bone marrow aspiration showed no invasion of lymphoma cells. This case was diagnosed as stage I according to the Lugano international conference classification. He underwent monotherapy using rituximab four times. However, the lesion did not respond. Therefore, radiotherapy was added which induced regression of the duodenal lesion. Follow-oup capsule endoscopy did not show any lesion in the distal ileum. As long-term outcome after treatment for duodenal follicular lymphoma is not known, strict observation is considered to be necessary.
