Colonic in situ mantle cell lymphoma.

This report describes the first case, to our knowledge, of in situ mantle cell lymphoma (MCL) in the gastrointestinal tract identified retrospectively by immunostains and fluorescence in situ hybridization (FISH) analysis after progression to disseminated disease with pleomorphic morphology several years later. A 45-year-old man with blood per rectum underwent colonoscopy and had random biopsies interpreted as benign colonic mucosa. Two years later, he presented with ileocolic intussusception related to enlarged lymph nodes. Biopsies on the second presentation demonstrated widespread MCL. Reevaluation of the original colonic biopsies showed cyclin D1-positive cells within small lymphoid aggregates, confirmed by FISH for t(11;14). Postchemotherapy, lymphoid aggregates in colonic biopsies showed scattered cyclin D1- and FISH t(11;14)-positive cells, similar to the original in situ lymphoma. We discuss this case in the context of the current understanding of the evolution of MCL and the difficulties associated with detecting primary GI lymphoma.