S3752 A Wolf in Sheep’s Clothing: A Rare Presentation of Colonic MALT Lymphoma in the Setting of Poorly Controlled Ulcerative Colitis

Introduction: Extranodal marginal zone lymphoma (EMZL) of Mucosa-Associated Lymphoid Tissue (MALT) is a rare form of non-Hodgkin's lymphoma, making up 8% of cases. While 70% are gastric, only 2.5% occur in the colon, accounting for 0.5% of colon cancers. The median age of diagnosis is 65-70, with chronic immune reactions from autoimmune or infectious stimuli as risk factors. Helicobacter pylori is linked to gastric MALT lymphoma, but no definitive risk factors exist for colonic EMZL. Endoscopic features vary, including superficial erosions, nodular masses, and subepithelial tumors. Clinical presentations range from asymptomatic to abdominal pain and hematochezia. We present a case of a young woman with treatment-refractory ulcerative colitis (UC) where incidental MALT lymphoma of the sigmoid colon and rectum was found during surveillance colonoscopy. Case Description/Methods: A 23-year-old woman presented for a second opinion about her ulcerative proctosigmoiditis. She had failed multiple 5-ASA products, azathioprine, in addition to vedolizumab and was steroid dependent for 2 years. Biweekly adalimumab was initiated due to insurance limitations. A colonoscopy performed 10 weeks later revealed persistent Mayo 2 disease activity. Sigmoid and rectal biopsies showed a diffuse lymphoplasmacytic infiltrate involving the lamina propria and extending into the muscularis propria, and immunohistochemical stains showed CD20 positivity with co-expression of BCL2. The overall findings were most consistent with involvement by marginal zone B-cell lymphoma in the setting of active colitis. Adalimumab was discontinued and rituximab was initiated. She subsequently underwent diverting ileostomy creation with plans for total colectomy. Discussion: This case highlights a rare presentation of MALT lymphoma superimposed on poorly controlled UC in a young patient on short term adalimumab. Colorectal MALT lymphoma is rare, accounting for less than 0.5% of colon cancers. Its endoscopic appearance can be variable, complicating identification. The optimal treatment is undefined but can include surgery, chemotherapy, or radiation. This case highlights the importance of considering lymphoma in poorly controlled UC patients, even in those without advanced age, prolonged disease, or on chronic immunosuppressive therapy. It also illustrates the importance of both targeted and non-targeted biopsies during surveillance colonoscopies in IBD, as endoscopic evaluation may not reveal suspicious lesions.