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The incidence of lymphoma has rapidly increased over the last 40 years in Japan, following a trend that is very similar to that of breast cancer. In particular, the relative frequency of follicular lymphoma (FL) has reached that in Western countries. Given its indolence, a "watch‐and‐wait" approach is often applied to FL patients. We have shown that FL is often detected in the second portion of the duodenum and has a distinct follicular dendritic cell distribution and heavy chain variable usage similar to mucosa‐associated lymphoid tissue (MALT) lymphoma. Although the t(14;18)(q32;q21) frequency is the same as in the nodal subtype of FL, there are also ongoing mutations, immunopositivity for cluster of differentiation 10 and B‐cell lymphoma (BCL)6, and overexpression of BCL2. Gene expression profiling has shown that it is more similar to gastric MALT lymphoma than to nodal FL. Duodenal‐type FL lacks the activation‐induced cytidine deaminase (AID) expression observed in nodal ones, although this may be compensated for by BTB domain and CNC homolog 2. Based on these findings, duodenal‐type FL has been included in the Revised 4th edition of the World Health Organization classification published in late 2017. [ABSTRACT FROM AUTHOR]

The gastrointestinal (GI) tract is the most commonly involved site of extranodal follicular lymphoma (FL). GI-FL shows very indolent clinical behavior and localized at GI tract without any progression or transformation compared to nodal FL. The most frequently involved site of the GI tract was the duodenum followed by the jejunum and ileum, and only 15% of FL arising in the second part of the duodenum were localized there without scattered very small daughter lesions in other GI tract examined by double-balloon endoscopy. The typical macroscopic appearance of GI-FL was multiple white nodules. Microscopically, neoplastic cells were small- to medium-sized lymphoid cells and formed neoplastic follicles. Most of the cases (>95%) were histologically Grade 1 to 2 (low grade). Several pathological and molecular characteristics were seen in GI-FL (especially duodenal FL) compared with nodal FL: immunoglobulin heavy chain deviation to VH4 and VH5; memory B-cell immunophenotype; and molecular features shared by mucosa-associated lymphoid tissue lymphoma. Considering the pathological and molecular uniqueness of this disease, GI-FL should be separately managed from nodal FL. [ABSTRACT FROM AUTHOR]

Follicular lymphoma ( FL) of the gastrointestinal tract, particularly duodenal follicular lymphoma ( DFL), is a rare variant of FL with indolent clinical behavior, and this disease is included in the 2008 World Health Organization classification system. In contrast to nodal follicular lymphoma ( NFL), DFL occurs most frequently in the second part of the duodenum, lacks follicular dendritic cell meshworks and has memory B-cell characteristics. However, its molecular pathogenesis is still unclear. In the present study, we examined 10 DFL, 18 NFL and 10 gastric MALT lymphoma samples using gene expression analysis. Quantitative RT- PCR experiments and immunohistochemical analysis for 72 formalin-fixed, paraffin-embedded tissues from an independent series, including 32 DFL, 19 gastric MALT lymphoma and 27 NFL samples, were performed for validation of microarray data. Gene expression profiles of the three lymphoma types were compared using 2918 differentially expressed genes ( DEG) and results suggested that DFL shares characteristics of MALT lymphoma. Among these DEG, CCL20 and MAd CAM-1 were upregulated in DFL and MALT but downregulated in NFL. In contrast, protocadherin gamma subfamily genes were upregulated in DFL and NFL. Quantitative RT- PCR and immunohistochemical studies demonstrated concordant results. Double immunofluorescence studies revealed that CCL20 and CCR6 were co-expressed in both DFL and MALT. We hypothesize that increased expression of CCL20 and MAd CAM-1 and co-expression of CCL20 and CCR6 may play an important role in tumorigenesis. [ABSTRACT FROM AUTHOR]