Primary gastrointestinal follicular lymphoma involving the duodenal second portion is a distinct entity: a multicenter, retrospective analysis in Japan.

We conducted a multicenter, retrospective study to determine the anatomical distribution and prognostic factors of gastrointestinal (GI) follicular lymphoma (FL). This study included 125 patients with stage I and II(1) GI-FL. Of the 125 patients, the small intestine was examined in 70 patients, with double-balloon endoscopy and/or capsule endoscopy. The most frequently involved GI-FL site was the duodenal second portion (DSP) (81%), followed by the jejunum (40%); 85% of patients with involvement of the DSP also had jejunal or ileal lesions. The absence of abdominal symptoms and macroscopic appearance of multiple nodules were significantly present in the DSP-positive group. During a median follow up of 40 months, six patients showed disease progression. Patients with involvement of the DSP had better progression-free survival (PFS) than those without such involvement (P = 0.001). A multivariate analysis revealed that male sex, the presence of abdominal symptoms, and negative involvement of the DSP were independently associated with poor PFS. In conclusion, most patients with GI-FL have duodenal lesions associated with multiple jejunal or ileal lesions. Gastrointestinal follicular lymphomas involving the DSP might be a distinct entity showing a favorable clinical course.