Colonic Mucosa-Associated Lymphoid Tissue Lymphoma Presented as Multiple Polyposis at Colonoscopy in a Nigerian Man: Case Report of a Rare Occurrence and Brief Review of Literature

Anatomically, mucosa-associated lymphoid tissue (MALT) is found in various parts of the body. In the colon, lymphoid tissue occurs mainly as isolated lymphoid follicles that are composed mainly of B lymphocytes. Such gastrointestinal tract MALT plays an important role in immune surveillance and mucosal regeneration, but the cells inMALTmayoccasionally undergo abnormal proliferation and give rise to lymphoma of the MALT type. The World Health Organization identifies these lesions of non-Hodgkin lymphoma as being of B-cell origin and classifies them as extranodal marginal zone B-cell lymphoma of the MALT type. In 1983, Isaacson and Wright were the first to describe the term MALT lymphoma. In the gastrointestinal tract, the most common site of occurrence is the stomach and small intestine; only rarely does MALT occur in the colon. To put its rarity in context, all colonic lymphomas account for approximately 0.2% to 0.6% of colorectal malignant tumors and only 2.5% of all lymphomas. Among the lymphomas seen in the colon, the most common type is diffuse large B-cell lymphoma, and MALT-type lymphoma accounts for , 20% of cases in this subgroup.