Follicular lymphoma with involvement of the splenic marginal zone: a pitfall in the differential diagnosis of splenic marginal zone cell lymphoma.

Follicular lymphomas (FL) involving the spleen arise in and expand the germinal centers of the white pulp, whereas mantle cell lymphomas arise in the mantle zone and surround the benign germinal center. The recently described marginal zone cell lymphoma (MZCL) is a B-cell neoplasm characterized by concentric expansion of cells around the follicle, with or without infiltration of the mantle zone or germinal center. In addition, the immunoglobulin heavy chain gene is rearranged although none of the MZCL reported have been shown to be positive for the bcl-2 gene translocation by molecular studies. We report a patient with FL showing preferential involvement of the marginal zone of spleen morphologically mimicking a primary splenic MZCL. The patient reported here had a well-documented previous lymph node diagnosis of FL. The immunoglobulin heavy chain gene and bcl-2 gene rearrangement analysis confirmed the clonal origin of both the original FL, as well as the lymphoma, with a marginal zone pattern in the spleen.