S4623 From the Antrum to the Anus: A Disseminated Case of GI Mantle Cell Lymphoma

Introduction: Mantle cell lymphoma (MCL) is rare and accounts for around 5% of cases of non-Hodgkin’s lymphoma, with an annual incidence of 1 of 200,000 individuals. It typically presents in the 6th and 7th decades of life with a 3:1 ratio of men to women. Systemic symptoms include fever, night sweats, weight loss, and fatigue. Gastrointestinal tract (GIT) involvement can present as diarrhea, abdominal pain, or occult bleeding. We present a patient presenting with unexplained anemia, subsequently found to have disseminated GI mantle cell lymphoma. Case Description/Methods: An 81-year-old White man with gastroesophageal reflux disease, iron deficiency anemia on oral iron, a pancreatic neuroendocrine tumor post pancreatectomy and splenectomy (2017), and prior transduodenal resection of a tubulovillous adenoma presented for ongoing anemia despite supplementation, without evidence of bleeding. Esophagogastroduodenoscopy revealed mucosal flattening and erosions in the gastric body and antrum, and at the duodenal major papilla. Colonoscopy identified a 3 cm submucosal non-obstructing oozing mass approximately 20 cm from the anal verge. Biopsies from these sites yielded neoplastic lymphoid proliferation involving the lamina propria and submucosa. Fluorescence in situ hybridisation confirmed a CCND1/IgH t(11;14) translocation consistent with MCL. TP53 was negative. Positron emission tomography (PET) scan showed enlarged reactive lymph nodes. The patient was started on acalabrutinib. Despite negative serial imaging, his anemia continued, with a later bone marrow biopsy revealing MCL as well. Discussion: MCL frequently involves extranodal sites, and the GIT is a recognized target. Involvement is often subclinical, emphasizing the importance of biopsies in areas even with mild abnormalities. Frequently involved GIT sites include the small intestine, colon, and stomach, sometimes manifesting as multiple lymphomatous polyposis (MLP). Our patient’s disease reflects proclivity for diffuse mucosal infiltration, with a large polypoid to subtle infiltrative lesions. Diagnosis is confirmed histologically and via immunophenotyping, revealing CD20+, cyclin D1+, and SOX11+ expression with characteristic t(11;14)(q13;q32) translocations. TP53 negativity may predict a favorable response, while positivity implies a disease with conventional chemoimmunotherapy resistance. This case highlights the value of biopsy in areas without overt lesions, considering MCL in older adults with unexplained anemia, and it reinforces the need for comprehensive staging, including PET-computed tomography and bone marrow biopsy, for guiding management.