Follicular lymphoma mimicking marginal zone lymphoma in lymph node: a case report

Nodal follicular lymphoma (FL) is typically composed of follicular or nodular proliferation of small cleaved lymphoid cells, presumably derived from germinal center (GC) B cells. The hallmark of FL is t(14;18)(q32;q21) chromosomal translocation, which juxtaposes anti-apoptotic gene BCL2 to immunoglobulin heavy chain (IGH) promoter. Reflecting this background, FL cells are immunohistochemically positive for BCL2 as well as GC B cell markers CD10 and BCL6. It is known that low grade B-cell lymphomas, including FL, chronic lymphocytic leukemia/small lymphocytic lymphoma, and marginal zone lymphoma, are sometimes associated with marginal zone differentiation or plasmacytic differentiation. The marginal zone differentiation obscures the morphological differences among these, providing diagnostic challenges for histopathologists. In this paper, we present a case of FL, originally mimicking marginal zone lymphoma in the axillary lymph node. Subsequent bone marrow biopsy showed paratrabecular infiltration of small to medium-sized lymphoid cells. Immunohistochemical analysis of the bone marrow biopsy together with histopathology and flow cytometry of the axillary lymph node led to a final diagnosis of FL with marginal zone differentiation in the axillary lymph node and its bone marrow infiltration. Our case illustrates and reconfirms the importance of clinicopathological correlation which leads to a correct diagnosis.