Primary gastrointestinal follicular lymphoma (FL) is a rare, indolent subtype of FL accounting for approximately 1-3% of primary GI lymphomas. The site most commonly involved is the second portion of the duodenum.
Histologically, compact, neoplastic follicles with attenuated/absent mantle zones are seen mainly in the lamina propria, with rare extension into the submucosa.
Similar to nodal FL, most GI FLs are positive for CD20, CD79a, CD10, BCL-6 and BCL-2. What is unique about duodenal FLs is the presence of the “hollow” pattern of staining seen with CD21 and CD23. This is due to the peripheral arrangement of the follicular dendritic cells with relative sparing of the follicular centre. In contrast, the follicular dendritic cells are scattered throughout the neoplastic follicles in nodal FL.
Cytogenetically, similar to nodal FL, duodenal FL is characterized by the t(14;18)(q32;q21) translocation between IgH and BCL2 genes, which is present in up to 90% of cases.
This slide shows BCL2 stain. See Related Content for H&E, CD20, CD10, BCL6, and CD23 stains.
Starova, B., Ghorab, Z. Duodenum, Follicular lymphoma, BCL2 stain. Digital Laboratory Medicine Library, Dept of Laboratory Medicine & Pathobiology, University of Toronto. Published
. Accessed December 17, 2025. https://dev.dlml.cflabs.ca/image/duodenum-follicular-lymphoma-bcl2-stain-lmp29228
