Aberrant bcl6 protein expression in patients with EMZL following recurrence or progression: case report of two cases.

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (EMZL) is an indolent B-cell lymphoma that can involve various anatomic sites. EMZL is derived from post-germinal center marginal zone B cells and typically lacks bcl-6 expression. Herein, we report two post-treatment cases of EMZL where unexpected bcl-6 protein expression was observed in specimens obtained following recurrence or progression. This contrasts with the primary specimens, which were negative for the bcl-6. Additionally, we confirm that the altered bcl6 expression observed in relapsed EMZL cases is independent of BCL6 gene rearrangement, as demonstrated by fluorescence in situ hybridization analysis. Relevant literature was reviewed and summarized to enhance the understanding of this phenomenon, particularly for pathologists.