Summary The genetic alterations underlying extranodal marginal zone B-cell lymphomas of mucosa-associated lymphoid tissue type are heterogeneous and show variation according to the tumor site. Here, we report a case of mucosa-associated lymphoid tissue lymphoma of the gallbladder with genetic characterization. This lymphoma, diagnosed in a 75-year-old woman who underwent cholecystectomy for suspected acute cholecystitis, presented as diffuse thickening of the gallbladder wall. The morphology was typical of mucosa-associated lymphoid tissue lymphoma, and by immunophenotype, the tumor cells were CD20+ CD5− CD10− CD23− CD43− BCL6− BCL2+ IgM+ IgD− λ +, with moderate nuclear expression of BCL10. Interphase fluorescence in situ hybridization analysis on paraffin sections, using a fusion probe for API2 / MALT1 , demonstrated 2 fusion signals in most nuclei, bringing the first documentation of a t(11;18)(q21;q21) in this exceptional primary disease location.
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