Histologic examples of nodal marginal zone lymphoma (NMZL), splenic marginal zone lymphoma (SMZL), and gastric extranodal marginal zone lymphoma (gastric MALT lymphoma). A. Whole mount of a lymph node with NMZL. A thickened capsule (lower left) and interfollicular infiltrate of small B lymphocytes and monocytoid B cells is shown. A reactive follicle (white arrow) is surrounded by an expanded marginal zone of monocytoid B cells while other follicles have been partially replaced by small B cells (black arrows and inset). B. Section of a spleen with SMZL showing marked expansion of the white pulp by monocytoid B cells (inset). Note the lack of follicular mantles and infiltration of monocytoid B cells into the splenic red pulp. C. Full thickness section of gastric MALT lymphoma showing an ulcerated epithelial surface and diffuse infiltrate of marginal zone cells in the lamina propria that have colonized the germinal centers of the B-cell follicles. Scattered lymphoepithelial lesions were also present (inset).