MALT Lymphoma : Immunophenotype

Comments:
MALT Lymphoma - Immunophenotype: MALT lymphomas are immunophenotypically similar to marginal zone B-cells. They are: CD20+, CD79a+, CD5- (occasional cases may be CD5+), CD10- (rare cases are CD10+ but BCL6-), CD23- and CD11c+/- (weak). On flow cytometry, the monoclonal B cells are sometimes masked by the benign germinal center cells or background polytypic B cells.

CD43 expression, which is indicative of a neoplastic phenotype, is seen in about 50% of cases. There are expanded follicular dendritic cell meshworks that can be visualized with CD21, CD23, and CD35 immunostains. These meshworks are often colonized and disrupted by the neoplastic cells.

The tumor cells are light chain restricted. With regards to heavy chains, most cases express IgM heavy chains, less commonly IgA or IgG and are negative for IgD. MNDA is a useful marker separating MALT lymphomas (positive in 60-75%) from follicular lymphomas (positive in <10% of cases). Ki-67 labeling index is low.

The immunohistochemical panel shown here is from a bladder MALT lymphoma which is CD20+, CD43+, and CD10-. CD3 shows background T-cells. The neoplastic cells are CD3-.