Histopathology of SMZL. In this typical case, (A) a nodular lymphoid proliferation with a biphasic appearance effaces the white pulp, infiltrates the wall of a great vessel (arrow) (hematoxylin and eosin [H&E] stain; magnification ×20) and extends to (B) the red pulp in a patchy distribution (CD79a; magnification ×100). (C) Morphologic pictures show medium sized, monocytoid lymphocytes with only scattered large cells (H&E stain; magnification ×400) and (D) a variable degree of plasmacytic differentiation (Giemsa stain; magnification ×400). (E) Anti-CD23 immunostain (magnification ×100) depicts the CD23⁺ marginal zone cells as well as the residual dendritic meshwork within the colonized follicles highlighted by (F) Mib/Ki-67 (magnification ×100), which confers a targetoid appearance. (G) A prototypical BM biopsy shows a small to medium size lymphoid population (Giemsa stain; magnification ×400) with (H) a nodular and sinusoidal distribution (CD20; magnification ×400). (G) Note the megaloblastoid features within the erythroblastic lineage, a common finding in cases associated with paraproteinemia and anemia.