Purpose: We report the case of an adolescent with a rectal MALT lymphoma manifesting with hematochezia who was treated successfully with radiotherapy. Pediatric gastrointestinal (GI) malignancies are very rare. Of these, lymphomas are the most common. In adults, primary GI non-Hodgkin lymphomas (NHL) account for 4-20% of all NHL. WHO classifies NHL as Burkitt's, diffuse large B cell, mantle cell, follicular cell, and extranodal marginal zone mucosa-associated lymphoid tissue lymphoma (MALT). Colorectal lymphomas are very rare (10-20% of GI NHL and 0.2-0.6% of all colonic malignancies), and only 10-25% localize in the sigmoid and rectum. MALT lymphomas represent 5% of NHL and the majority occur in the stomach. MALT rectal lymphomas are extremely rare and have been treated with surgery, chemotherapy, antibiotics, or radiation therapy. A 16-year-old male presented with a history of painless hematochezia and constipation for 2 months. Past medical and family history were unremarkable. Rectal exam revealed redundancy of the posterior rectal mucosa and gross blood on the glove. The physical exam was otherwise normal. Colonoscopy was normal except for mild nodularity of the rectosigmoid, with cobblestoning of the first 5 cm of the rectum and the presence of two hypertrophic anal papillae. Biopsies of the first 5 cm of rectum, including the anorectal junction, showed an infiltrate of large atypical B cells CD20+, Pax 5+, CD 79a+, CD43+, MUM1+, BCL2+, BCL6+, CD5-, CD10-, BCL1-. Plasma cells were CD20- showing cytoplasmic IgA kappa restriction. CD79a was strongly expressed in plasmacytic cells and poorly in B cells. Ki67 proliferation index was low to moderate. EBER-ish was negative. The findings were consistent with marginal zone lymphoma with plasmacytic differentiation. PET scan showed a hypermetabolic uptake in the anal region (SUV 11.4). CT of the chest, abdomen and pelvis was negative. The patient received 24 GCE involved field proton beam radiotherapy in 12 fractions to the anorectal lesion. Pelvic and inguinal nodes were not irradiated. Repeat PET scan 5 months after radiotherapy showed decreased anal hypermetabolic uptake (SUV 4.4). Colonoscopy after 6 months showed mild nodularity of rectosigmoid. The anorectal margin had mild erythema and nodularity. Rectal biopsies showed benign lymphoid aggregates and the anorectal junction mucosa was normal. He reported occasionally minor anorectal bleeding when constipated. To our knowledge this is the first pediatric case of a rectal MALT lymphoma that was induced into remission by low dose proton beam radiotherapy. Although very rare, anorectal malignancies should be considered in the differential diagnosis of hematochezia in children and adolescents.
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