IRTA1 expression in extranodal marginal zone (MALT) lymphoma is variable across anatomic sites

Abstract Objective Immune receptor translocation-associated 1 (IRTA1) expression, which has recently been shown to be highly specific for marginal zone lymphoma, is found in only a subset of extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma). In this study, we examined whether IRTA1 expression in MALT lymphoma was dependent on anatomic location. Methods IRTA1 immunohistochemistry was performed in 60 cases of extranodal MALT lymphoma, arising at breast, conjunctiva, lung, salivary gland, skin, and stomach (10 cases each). Expression was also scored with respect to detailed morphologic features. Results IRTA1 staining was identified in 25 (42%) cases, ranging from 9 (90%) of 10 in lung to 2 (20%) of 10 in gastric MALT lymphoma. IRTA1 staining was not characteristic of specific morphologic features, as it was absent in most lymphoepithelial lesions, perifollicular cells, cells with overt monocytoid cytology, and plasmacytic cells. IRTA1 expression was also identified in 5 (50%) of 10 cases of pulmonary nodular lymphoid hyperplasia. Conclusions IRTA1 expression is heterogeneous in extranodal MALT lymphoma. Staining for IRTA1 is not characteristic of specific morphologic features, but varies with the anatomic site of disease. Knowledge of site-specific differences in MALT lymphomas will facilitate diagnosis in routine clinical practice.