Morphological and immunohistochemical features of extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) of ocular adnexal. A) Monotonous population of small centrocytic cells with scant cytoplasm (ocular adnexal section HE, ×200 magnification), B) MALT lymphoma cells express CD20 (+).There are scattered glands of ocular adnexal (red stars in all figures) (CD20 immunostain ×200 magnification), C) MALT lymphoma with few lymphoepithelial lesions - the tumour cells infiltrate the glands (red arrow) (CD20 immunostain ×400 magnification), D) MALT lymphoma with low number of normal T CD3 (+) lymphocytes (CD3 immunostain ×400 magnification). In addition to the figures, the lymphoma cells are negative for CD43 (−) and CD5 (−). Plasmacytic differentiation is present in approximately 20% of MALT cells with CD138 (+) expression on this subpopulations of lymphoma cells. Tumour cells show kappa (+)/lambda (−) light chain restriction by immunohistochemical reaction.