In order to compare primary gastro-intestinal (GI)
B-cell lymphomas histomorphologically and immunophenotypically with orthologous steps of B-cell differentiation within the mucosa-associated lymphoid tissue (MALT) of the GI tract, a comprehensive panel of well characterized leucocyte
differentiation antigens was composed. It comprised
immunoglobulin constituents CD5, CD10, CD11c, CD20, CD23, CD24, CD30, CDw32, CD38, CD39, CDw75, CD76, and
vimentin. These
antigens yield characteristic immunoprofiles for the following B-cell compartments of the MALT, per se closely linked to cytologically distinct B-cell phenotypes: mantle zone (MZ), extrafollicular compartment (EF), follicle center (FC), and plasma-cell compartment (PC). An unselected series of 31 MALT B
lymphomas (13 of low and 18 of high grade
malignancy) was classified histologically in routine preparations and subsequently characterized immunohistochemically using fresh frozen tissue,
monoclonal antibodies (MAbs) against the
antigen panel listed above, and an indirect immunoperoxidase method. The final classification considered both morphology and immunoprofile of
tumor cells. Ten
tumors were "typical" in both respects: 2 closely corresponded to MZ, 5 to
EF, 2 to FC and 1 to PC. The remaining 21 cases were characterized as "atypical" because of anaplastic cytology and/or abnormal co-expression and/or loss of
antigens. A hybrid EF/FC phenotype was most frequently observed together with centrocyte-like or centrocytic anaplastic cytology of
tumor cells. We conclude that MALT B-cell
neoplasia comprises a broad spectrum of histo- and immunophenotypes ranging from well differentiated forms closely mimicking normal B-cell development to highly abnormal
tumors which cannot be subclassified.