Introduction
Mucosa-associated lymphoid tissue (MALT) lymphoma is a subtype of non-Hodgkin lymphoma that can occur in the gastrointestinal tract, most commonly in the stomach and small intestine. Colorectal MALT lymphomas account for only 2.5% of MALTomas and do not have a clear association with Helicobacter pylori infection. Treatment strategies are not standardized given the rarity of the condition and include observation, endoscopic resection, surgery, radiotherapy, chemotherapy, immunotherapy, or a combination thereof. Endoscopic resection techniques, such as endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD), are potential treatment options for select colorectal MALT lymphomas, and their use is limited to early-stage, superficial neoplasms.

Case reports
Case 1: An 80-year-old man underwent routine screening colonoscopy and biopsy of a 2-cm, atypical-appearing, polypoid lesion in the proximal transverse colon. Pathology showed MALT lymphoma and additional work-up showed no lymphadenopathy or bone marrow involvement. Upper endoscopy was negative for Helicobacter pylori. After multidisciplinary discussion, it was elected to proceed with endoscopic removal of the lesion via EMR (Figure 1). Pathology confirmed MALT lymphoma with Ki-67 of <5%. Follow-up colonoscopy at 1 year and biopsy of the post-resection scar showed no residual disease.

Case 2: A 47-year-old man underwent routine screening colonoscopy and biopsy of a large, slightly polypoid area with abnormal mucosal pattern at the hepatic flexure. The lesion appeared to involve at least 50% of the luminal circumference and extended over several folds. Pathology demonstrated B-cell lymphoma, favored to be MALT lymphoma. A urea breath test and PET-CT imaging were negative. After multidisciplinary discussion, it was elected to proceed with an attempt at ESD but the latter was aborted given the indistinct margins and inability to delineate the boundary of the lesion despite utilization of enhanced imaging (Figure 2). A partial colectomy is planned.

Discussion
The management of colorectal MALT lymphomas is not evidence-based due to its uncommon occurrence. Treatment of colorectal MALT lymphomas requires a multidisciplinary approach and exclusion of extra-colonic involvement. Endoscopic resection can be considered for isolated, small superficial MALTomas with distinct boundaries, but is not suitable for large lesions with ill-defined borders given the risk for incomplete resection. In patients who undergo endoscopic resection, periodic follow-up with colonoscopy and biopsy is warranted.

Figure 1
A) 2-cm polypoid lesion with abnormal mucosal pattern and relatively distinct border
B) Complete lesion removal via wide-field EMR

Figure 2
A) Large slightly polypoid lesion with abnormal mucosal pattern and indistinct margins
B) Lesion boundary remains indeterminate on narrow-band imaging

Elida Voth

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