MONOCYTOID MARGINAL ZONE B-CELL DIFFERENTIATION IN FOLLICLE CENTER CELL LYMPHOMA/

We report on two cases of low grade follicle centre cell lymphoma with a pronounced parafollicular monocytoid/ marginal zone B-cell componen t. One patient had a history of preceeding follicular high grade B-cel l lymphoma of centroblastic type showing the same light chain restrict ion and identical immunoglobulin heavy chain gene rearrangement as the low grade lymphoma diagnosed 15 months later, Morphologically, in bot h cases the two constituents of the low grade tumours were clearly dis tinguishable. Immunohistochemically, the follicular component strongly expressed bcl-2 protein in contrast to a weak staining of the margina l zone B-cell component. Performing PCR, a rearrangement of the major breakpoint region of bcl-2 was not found. Identical light chain restri ction of the follicular and the monocytoid B-cell/marginal zone compon ents strongly indicates a clonal relationship between them, A monocyto id/marginal zone B-cell component in follicular lymphoma probably resu lts from differentiation of the follicle centre cells and does not ind icate a composite lymphoma.