IRTA1 and MNDA Expression in Marginal Zone Lymphoma: Utility in Differential Diagnosis and Implications for Classification.

Objectives: To evaluate the clinical utility of immune receptor translocation-associated protein 1 (IRTA1) and myeloid nuclear differentiation antigen (MNDA) expression in the diagnosis and classification of marginal zone lymphomas (MZLs).

Methods: IRTA1 was examined using a novel RNA in situ hybridization assay and MNDA expression determined by immunohistochemistry in 127 small B-cell neoplasms, including 80 cases of MZL.

Results: IRTA1 expression was detected in 31 (42%) of 74 MZLs vs one (2%) of 43 other small B-cell neoplasms (P < .001). MNDA staining was positive in 51 (64%) of 79 MZLs vs 21 (45%) of 46 non-MZLs (P = .06). MNDA expression was particularly uncommon in follicular lymphoma (3/14, 21%; P = .003 vs MZL). There was no association between MNDA and IRTA1 expression and the presence of monocytoid cytology. IRTA1 expression was less frequent in cases with a diffuse growth pattern.

Conclusions: IRTA1 and MNDA are useful markers in the differential diagnosis of MZLs.