Marginal zone cell lymphoma--an update on recent advances.

The marginal zone represents one of the distinct compartments of the B-cell area in lymphoid tissues. It is especially well developed in the spleen and in Peyer's patches of the gut, but not in lymph nodes, with the exception of the ones in the mesenterium. However, the pronounced proliferation of so-called 'monocytoid B-cells' that may be seen in some inflammatory conditions of the lymph node may be regarded as a nodal reactive marginal zone cell expansion. The cellular compositions of the marginal zone and the monocytoid B-cell proliferation are similar and both show a heterogeneous population of B-cells, of which the functions are being slowly unravelled. Neoplasms originating in the marginal zone have been recognized in the past and are listed in the REAL classification as marginal zone B-cell lymphomas including extranodal MALT-type lymphomas, splenic marginal zone lymphomas and nodal (monocytoid) marginal zone lymphomas. Marginal zone cell lymphomas display a broad morphological spectrum, which is reflected by the heterogeneity of the cellular composition and the variation in the growth pattern of the lymphoma, but is independent of the anatomical site. All three marginal zone cell lymphomas share immunophenotypic, genetic and chromosomal similarities which will be discussed. The morphologic features are dealt with only briefly as they have been extensively discussed elsewhere.