S3810 The Road Less Traveled: Rectal Metastasis of Prostate Adenocarcinoma

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Introduction: Mucosa-associated lymphoid tissue lymphoma (MALT) lymphoma, or MALToma, is a rare type of B-cell non-Hodgkin lymphoma which most commonly presents in the stomach, however may arise in different organs such as the small intestine, parotid gland, thyroid gland, colon, and elsewhere. Colonic MALTomas account for only 2.5% of all MALTomas and 5% of non-Hodgkin lymphomas. Due to its rarity, we present this case. Case Description/Methods: An asymptomatic 86 year-old man underwent routine screening colonoscopy recently which revealed 6 seemingly benign polyps and diverticulosis throughout the colon. His previous colonoscopy was normal, except for 1 tubular adenoma which was removed. He denied any symptoms in totality including constipation, diarrhea, and hematochezia. Laboratory results were unremarkable, except for mildly decreased platelets and slightly elevated blood urea nitrogen and creatinine, likely attributable to his past medical history of chronic kidney disease. The histopathology report indicated that 1 of the 6 polyps, which was a 10 mm polyp resected from the sigmoid colon via hot snare, depicted an atypical B-cell lymphoid aggregate on microscopy. A further panel of immunohistochemical stains was performed which showed strong CD20 positivity in the vast majority of the lymphocytes with dim co-expression of CD43 indicative of MALT lymphoma. There was also CD21 highlighting in small residual dendritic follicular networks. Computed tomography (CT) scan of chest, abdomen and pelvis is scheduled to assess for spread to any other tissues. An upper endoscopy will also be done to rule out the presence of a gastric MALToma. Helicobacter pylori testing is under consideration as part of a comprehensive workup, despite its stronger association with gastric MALTomas. Treatment is not unanimous but may include immunotherapy such as rituximab, chemotherapy, and/or H. pylori eradication. Discussion: MALT lymphomas are an uncommon subset of non-Hodgkin lymphoma which primarily occur in the stomach but may occur in the lungs, ocular adnexa, small intestine, or colon as well. Colonic MALToma are commonly detected on routine screening colonoscopy and have a median age of presentation of 60 years old. They frequently appear endoscopically as benign sessile polyps. This case testifies to the importance of colonoscopy screenings due to the asymptomatic nature and benign appearance of MALTomas.

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