Abstract
Follicular lymphoma （FL） is a low-grade B-cell lymphoma with an indolent clinical course, although histological transformation （HT） worsens the prognosis. Duodenal-type follicular lymphoma （DFL） is a type of FL that was recently introduced to the World Health Organization classification in 2017. Although the risk of HT in DFL is low, there have been few reports on its incidence. Further studies on the incidence of HT in DFL will provide useful information for establishing therapeutic strategies. Patients with DFL were followed for a long time, and their intestinal biopsies were examined to detect histological changes and study the incidence of HT in DFL. Twenty patients with FL in the duodenum or small intestine and stage I FL of the Lugano classification were studied. Specimens were stained with hematoxylin and eosin and examined morphologically. In addition, an immunohistochemistry assay was performed. All patients had FL histological grade 1-2 at the time of diagnosis. The median follow-up period was 56 months （range: 12-147 months）. There was no evidence of clinical progression or HT in any of the included patients. We detected a very low incidence of HT in DFL. Despite the limited number of patients studied, treatment for nodal FL may be unnecessary and even hazardous in patients with DFL.
