S3915 Primary Colonic MALT Lymphoma

Introduction: Mucosal-associated lymph tissue (MALT) lymphoma, also known as extranodal marginal zone lymphoma (EMZL), is a rare type of B-cell non-Hodgkin lymphoma often found in the stomach. Colonic EMZL is very rare and only documented in case reports. Its pathogenesis remains unclear, although chronic antigenic stimulation, inflammatory bowel disease, and immune dysregulation are potential contributing factors. We present a case of isolated colonic EMZL. Case Description/Methods: A 48-year-old woman with hypothyroidism presented for screening colonoscopy. She lost 15 lbs over 9 months while on semaglutide and reported nightly hot flashes with diaphoresis, which she attributed to menopause. Colonoscopy found 5 sub-centimeter sessile polyps in the cecum, transverse, and descending colon. Pathology revealed B-cell lymphoma (BCL) consistent with EMZL without diffuse large BCL (DLBCL) transformation. Upper endoscopy showed no pathologic evidence of H. pylori infection. Primary colonic EMZL was diagnosed when workup revealed no extracolonic involvement on positron emission tomography/computed tomography and no bone marrow involvement. Oncologic evaluation deemed it to be a slow-growing, incurable, but treatable lymphoma. Given her staging, observation was favored over single-agent non-curative rituximab. She has had a normal 1 year surveillance colonoscopy. Discussion: Primary colonic EMZLs are extremely rare with presentations varying from asymptomatic to GI bleeding, ileocecal intussusception, and intestinal obstruction. The etiology of colonic EMZL is unclear. H. pylori has been linked to lymphomagenesis in gastric MALT lymphoma due to persistent inflammation, and its eradication can lead to lymphoma regression in a majority of early-stage cases. Other infectious agents include Chlamydia psittaci, Achromobacter xylosoxidans, and Hepatitis C in various different organs. A subset may also demonstrate BIRC3/MALT1 fusion and IGH/IGK gene rearrangements. Our patient had neither H. pylori nor genetic alterations. There are no standardized treatment regimens. Endoscopic resection or systemic chemotherapy can be considered based on disease burden, systemic involvement, and DLBCL transformation. In a single case series, 80% of patients had no clinically evident disease after observation or radiation/chemotherapy. This case reminds endoscopists that not all mucosal polyps are adenomas or serrated lesions, and that MALT can exist exclusively in the colon even in the absence of H. pylori infection.