Extranodal marginal zone B cell lymphomas of the uvea: an analysis of 13 cases

The majority of primary lymphoproliferative lesions of the uvea represent low-grade B cell lymphomas and often display a prominent plasmacellular differentiation. The purpose of the current study was to classify the uveal lymphoproliferations according to the REAL classification; examine the immune profile of the plasmacellular differentiated tumour cells using the plasma cell-related antigens multiple myeloma oncogene-1-protein (MUM1), Vs38c, CD38 and CD138; and to compare this profile with that of mature reactive plasma cells. Following fixation, 13 lymphoproliferative lesions of the uvea were categorized on the basis of their morphology and immunophenotype according to the REAL classification. Included in the immunohistochemistry were B cell-specific activator protein (BSAP), MUM1, Vs38c, CD38 and CD138. Nested polymerase chain reaction (PCR) was also performed on DNA extracted from paraffin sections for the detection of gene rearrangements of the heavy immunoglobulin chain (IgH). All of the 13 uveal tract lymphoproliferative lesions represented malignant lymphoma of B cell non-Hodgkin type and could be diagnosed as 'extranodal marginal zone B cell lymphomas' (EMZL). The degree of plasmacellular differentiation varied between the tumours. In contrast to their non-plasmacytoid counterparts, the 'plasmacytoid' EMZL tumour cells were negative for the B cell markers CD20 and BSAP, and demonstrated heterogeneous positivity for the markers MUM1, Vs38c, CD38 and CD138. The most consistent marker was MUM1, being observed in all tumours. Co-expression of all plasma cell markers was observed in four (31%) uveal EMZL. Loss of CD138 expression was observed in six (46%) tumours, of Vs38c expression in five (38%) and of CD38 in one (7%) tumour. Although the diagnosis of malignant lymphoma was unequivocally based on morphological and immunophenotypical features, the molecular analysis was able to demonstrate clonal B cell populations in only one uveal EMZL. All uveal lymphoid proliferations investigated represented EMZL, with the corresponding morphology and immunophenotype as seen in EMZL in other extranodal locations. MUM1, followed by CD38 expression, were the most constant plasma cell antigens in the plasmacytoid EMZL tumour cells, with both Vs38c and CD138 positivity being lost in many tumours. Aberrant immune profiles of plasma cell-related antigens may be of help in the establishment of malignancy in uveal lymphoproliferative lesions, particularly where interpretation of light chain expression and/or PCR results is difficult.