MULTIPLE POLYPOID LESIONS OF PRIMARY MUCOSA-ASSOCIATED LYMPHOID-TISSUE LYMPHOMA OF COLON

Aims: This study was focused on unusual cases of mucosa-associated lym phoid tissue (MALT) lymphoma presenting with multiple polypoid lesions of the colon and rectum with a special reference to the differential diagnosis of mantle cell lymphoma. Methods and results: The lesions of these five cases grossly showed a segmental distribution of nodular p rotrusions in three patients and of innumerable small polyps in two. T hese patterns of involvement simulated those of multiple lymphomatous polyposis, known as the gastrointestinal presentation of mantle cell l ymphoma (MCL), and caused a differential diagnostic problem between MA LT lymphoma and MCL, which have different prognostic and therapeutic i mplications. Their histological features are almost indistinguishable from each other, especially in the small biopsy specimens via endoscop e, The most important procedure for their differentiation is cyclin D1 immunohistochemistry and its negative reaction provides strong indica tion of MALT lymphoma, Of interest, one case showed a rare karyotypic abnormality of t(11;18)(q21;q21), which has been reported specifically in MALT lymphoma. Conclusions: This study has indicated that the mult iple polypoid lesions of the colon occur not only in MCL, but also in MALT lymphoma, making differential diagnosis between the two entities necessary, and cyclin D1 immunohistochemistry is indispensable for dis tinguishing between them.