SPLENIC MARGINAL ZONE EXPANSION IN B-CELL LYMPHOMAS OF GASTROINTESTINAL MUCOSA-ASSOCIATED LYMPHOID TISSUE (MALT) IS REACTIVE AND DOES NOT REPRESENT HOMING OF NEOPLASTIC LYMPHOCYTES

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Abstract
It has been suggested that lymphocytes of mucosa-associated lymphoid tissue (MALT) arise from marginal zone cells and that MALT-derived lymphomas may spread to other extra-nodal sites by homing to marginal zones in different tissues.1 Marginal zone expansion has been observed in spleens removed during surgery for gastrointestinal MALT lymphoma, which was sufficiently extreme in some cases to suggest neoplastic involvement. To investigate this phenomenon, polymerase chain reaction (PCR) amplification of immunoglobulin heavy chain gene fragments was performed to demonstrate B-cell clonality in gastrointestinal MALT lymphomas and spleens from 11 patients. Monoclonal PCR products were obtained from 9 of the 11 gastrointestinal tumours but from none of the accompanying spleens. One additional spleen, for which the accompanying gastric lymphoma tissue was unavailable for review, yielded a monoclonal product. However, obvious lymphoma deposits were present in this specimen, in addition to marginal zone enlargement. It is concluded that splenic marginal zone expansion accompanying gastrointestinal MALT lymphoma is correctly interpreted as being reactive. Splenic involvement by MALT lymphoma is uncommon and does not show preferential colonization of the marginal zone to suggest homing of MALT-derived cells to this site.