S4846 Incidental Detection of Extranodal Mantle Cell Lymphoma During Evaluation for Chronic Colitis Symptoms

Introduction: Mantle cell lymphoma (MCL) is a rare subtype of non-Hodgkin lymphoma, accounting for approximately 3%–7% of cases. While it mainly involves the lymph nodes, MCL can also affect extranodal sites such as the gastrointestinal (GI) tract, blood, and bone marrow. When the GI tract is involved, MCL may present with symptoms that mimic an inflammatory bowel disease flare. We present an unusual case of extranodal MCL discovered incidentally during the evaluation of a patient with known ulcerative colitis. Case Description/Methods: A 77-year-old man with a 7-year history of ulcerative colitis controlled on mesalamine single treatment. He presented with complaints of persistent lower abdominal pain, rectal bleeding, and Diarrhea. On examination, he was afebrile with mild tenderness on palpation of the lower abdomen. A contrast-enhanced computed tomography of the abdomen and pelvis revealed interval development of retroperitoneal adenopathy suggestive of malignancy. A subsequent positron emission tomography/computed tomography scan showed hypermetabolic activity in both the retroperitoneal and mesenteric lymph nodes. There was also evidence of a distal sigmoid/rectal interface constriction, along with diffuse prostate involvement. Endoscopy and Colonoscopy was performed and Sigmoid colon biopsies were taken showing chronic active colitis with prominent lymphoid aggregates but no overt signs of malignancy. Immunohistochemical studies done on the biopsy samples revealed a diffuse, monomorphic lymphoid infiltration consistent with MCL, expressing CD20+, CD5+, Cyclin D1+, and SOX-11+ markers, with a low Ki-67 proliferation index (10%). Genetic testing revealed p53 negativity, supporting the low-grade nature of the lymphoma. The lymphoma was confined to extranodal sites without evidence of systemic spread, and the staging indicated localized disease. Given the indolent nature of the disease and the patient’s asymptomatic state at that time, a decision was made to initiate a “wait-and-watch” approach, with close follow-up and serial imaging. Discussion: The GI tract is a common site of extranodal involvement in MCL. While the colon is most frequently affected, MCL can involve any part of the GI tract. Endoscopically, the classic presentation is multiple lymphomatous polyposis. However, in our case, this characteristic finding was absent, indicating the diagnostic challenge in such presentations. Accurate diagnosis of MCL relies on histopathological evaluation and immunohistochemical staining.