S4111 When Routine Saves Lives: Incidental Finding of Mantle Cell Lymphoma During Screening Colonoscopy

Introduction: Mantle cell lymphoma (MCL) is a rare subtype of non-Hodgkin lymphoma that often involves lymph nodes, spleen, bone marrow, and gastrointestinal (GI) tract. However, primary colonic involvement is extremely uncommon, representing only about 2% of primary GI lymphomas. Because of its rarity and often nonspecific presentation, MCL of the colon may go unrecognized, particularly in asymptomatic individuals. We present a case on MCL in a patient that was completely asymptomatic as he underwent his first screening colonoscopy. This case illustrates the importance of routine screening colonoscopies, even in younger individuals without GI symptoms or family history of colon disease. Case Description/Methods: A 45-year-old man with no family history of colon cancer and no significant GI complaints was referred for routine screening colonoscopy. The examination revealed multiple submucosal lesions throughout the colon. Notably, a 5 × 5 cm superficially ulcerated mass was found in the cecum, partially obstructing the ileocecal valve. An 8 mm submucosal nodule was identified in the ileum 5 cm from the valve, along with numerous additional nodules (3–30 mm) across the colon, many with a yellow hue and central umbilication. No bleeding was observed. Cold forceps biopsies were obtained. Histopathology revealed a dense lymphoid infiltrate composed of neoplastic B cells expressing CD5, CD20, Cyclin D1, and SOX-11, The Ki-67 proliferation index was elevated (40%–50%), and Fluorescence in situ hybridization confirmed t(11;14) (q13; q32), TP53 mutation testing was negative, establishing the diagnosis of mantle cell lymphoma. Positron emission tomography and computed tomography imaging demonstrated mild diffuse adenopathy, possible gastric involvement, and splenomegaly. The patient was initiated on alternating cycles of R-CHOP-Zanubrutinib and R-DHAOx and is currently responding well to therapy. Discussion: This rare case of colonic MCL identified during a routine screening colonoscopy in an asymptomatic, average-risk 45-year-old underscores the critical diagnostic value of early screening. It highlights the need for clinician awareness of atypical presentations of GI lymphomas and supports maintaining a high index of suspicion even in patients without classical risk factors.