Non-germinal center diffuse large B-cell lymphoma arising from a common origin of duodenal-type follicular lymphoma.

Duodenal-type follicular lymphoma (DFL) is a rare subtype of follicular lymphoma (FL) characterized by a remarkably indolent clinical course. However, histological transformation to diffuse large B-cell lymphoma (DLBCL) has been sporadically reported, and its clinicopathological features remain poorly understood. We describe a rare case of DFL that transformed to non-germinal center DLBCL, including the specific biological characteristics based on immunohistochemical, cytogenetic, and molecular analyses. A 62-year-old woman was diagnosed with DFL and followed without treatment. Six years later, she presented with progressive anemia and an ulcerative lesion in the ileocecum. Biopsy confirmed the diagnosis of DLBCL with the non-GCB immunophenotype according to Hans' algorithm, which is an uncommon immunophenotype of transformed FL. Fluorescence in situ hybridization analysis revealed BCL6 translocation in both DFL and DLBCL samples. In addition, polymerase chain reaction and sequencing analyses of immunoglobulin heavy and light chain rearrangements clearly demonstrated that the DFL and DLBCL share a common origin. After surgical resection of the ileocecal lesion and six cycles of R-CHOP chemotherapy, the patient has remained in complete remission for 3 years. This case highlights the importance of long-term follow-up of DFL and provides insights into the pathophysiology underlying the transformation of DFL.