An unusual finding at screening colonoscopy: polypoid follicular lymphoma with marginal zone differentiation.

went screening colonoscopy after positive fecal occult blood testing (FOBT) during participation in the UK national bowel cancer screening program. Colonoscopy revealed clusters of sessile polypoid masses involving the rectum, sigmoid colon, cecum, and terminal ileum (●" Fig. 1, ●" Video 1). The largest lesion affected the cecum and measured about 7 cm across. Histopathological examination demonstrated abnormal lymphoid proliferation, consisting of irregular follicles with mantles and abnormal germinal centers. Immunohistochemistry showed predominant B-cell presence. Staining for CD10 and BCL6was negative, with κ light-chain restriction in nodule peripheries: these features favored a diagnosis of extranodal B-cell lymphoma, marginal zone subtype. Staging bonemarrow biopsy showed 25% B-cell lymphoma involvement and cytogenetics of marrow cells highlighted IgH-BCL2 translocation, typical of follicular lymphoma. Computed tomography demonstrated diffuse lymphadenopathy, splenomegaly, and thickening of the cecum associated with largemesenteric nodes (●" Fig. 2). Upper gastrointestinal endoscopy and biopsies were unremarkable, and Helicobacter pylori tests were negative. Immunohistochemistry of an axillary node biopsy confirmed predominant B-cell infiltration and, unlike the lower gastrointestinal histopathology, showed focal positivity for CD10 and BCL6, favoring the diagnosis of follicular lymphoma. Immunohistochemistry of further, larger colonic biopsies unified a final diagnosis of follicular lymphoma with marginal zone differentiation (●" Fig. 3) and confirmed common clonal origin. The overall clinical diagnosis fulfilled the criteria [1] for follicular lymphoma, stage An unusual finding at screening colonoscopy: polypoid follicular lymphoma with marginal zone differentiation