[NODAL MARGINAL ZONE B-CELL LYMPHOMA]. Primary nodal marginal zone lymphoma is a rare B-cell neoplasm usually seen in adults. In initial stages expansion of the follicular marginal zone is seen with or without attenuated follicular mantle zones. In later stages expansion of neoplastic marginal zone B-cells causes colonization of follicles with diffuse effacement of nodal architecture. In this example a few residual germinal cells can be identified (long arrow) but most of the cortex shows a diffuse architecture (big arrow).
[NODAL MARGINAL ZONE B-CELL LYMPHOMA]. A single almost naked germinal center (long arrow) is present surrounded by neoplastic marginal zone cells (left arrowhead). Neoplastic marginal zone B-cells extend beyond the follicular boundary into the interfollicular zone (right arrowhead). With further growth residual germinal centers become completely colonized and obliterated by neoplastic marginal zone B-cells. The only telltale sign of obliterated follicles is the presence of follicular dendritic cells as identified by CD21 immunostain.
[NODAL MARGINAL ZONE B-CELL LYMPHOMA]. More than 50% of cases of nodal MZL show coexpression of CD43 on neoplastic B-cells. However, residual germinal-center B-cells do not stain for this marker (arrow in the center). Coexpression of CD43 may also be seen in small lymphocytic lymphoma and mantle cell lymphoma but almost never seen in follicular lymphoma.
[NODAL MARGINAL ZONE B-CELL LYMPHOMA]. Immunostaining for CD21 shows follicular dendritic cells network of residual follicles. Note the lymphoma cells are negative.
[NODAL MARGINAL ZONE B-CELL LYMPHOMA]. Immunostaining for bcl-2 shows negative staining in germinal center B-cells confirming their benign nature whereas the neoplastic marginal zone B-cells are diffusely positive.
[NODAL MARGINAL ZONE B-CELL LYMPHOMA]. The lymphoma cells are small, uniform, and are admixed with monocytoid B-cells, transformed larger B-cells, and plasma cells. The monocytoid B-cells are slightly larger than small lymphocytes and contain abundant pale to clear cytoplasm resembling “monocytes.” The plasma cells may be so numerous as to obscure the true identity of the lymphoma with a differential diagnosis of lymphoplasmacytic lymphoma, nodal plasmacytoma or reactive plasmacytosis. Because of the presence of benign germinal centers in this lymphoma it is easy to discount the presence of plasma cells as reactive plasmacytosis.
[NODAL MARGINAL ZONE B-CELL LYMPHOMA]. The typical marginal zone B-cells are small lymphocytes with round to centrocytes-like nuclei without prominent nucleoli and moderate pale to clear cytoplasm. Cells with more abundant cytoplasm and larger convoluted nuclei are referred to as “monocytoid B-cells.” Marginal zone B-cells express pan B-cell markers CD19 and CD20 without coexpression of CD5, CD10, or CD23 (some cases express CD23).