A usually indolent mature B-cell lymphoma, arising from the marginal zone of lymphoid tissues. It is characterized by the presence of small to medium sized atypical lymphocytes. It comprises three entities, according to the anatomic sites involved: extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue, which affects extranodal sites (most often stomach, lung, skin, and ocular adnexa); nodal marginal zone B-cell lymphoma, which affects lymph nodes without evidence of extranodal disease; and splenic marginal zone B-cell lymphoma, which affects the spleen and splenic hilar lymph nodes, bone marrow, and often the peripheral blood. [from
NCI]