S3767 A Rare Case of Primary Rectal MALT Lymphoma Detected During Routine Screening

Introduction: Primary rectal neoplasms encompass a range of malignancies, most commonly adenocarcinoma, followed by squamous cell carcinoma and neuroendocrine tumors. Rectal lymphomas are exceptionally rare, accounting for about 0.05% of all primary rectal carcinomas. Primary gastrointestinal (GI) lymphomas are often associated with ulcerative colitis, typically as a consequence of prolonged immunomodulatory therapy. Additional risk factors include Helicobacter pylori infection, celiac disease, and immunodeficiency states such as human immunodeficiency virus (HIV) infection. We report a rare case of mucosa-associated lymphoid tissue (MALT) lymphoma of the rectum identified during routine colorectal cancer screening in a patient without identifiable risk factors. Case Description/Methods: A 46-year-old woman with a medical history of generalized anxiety disorder presented for routine colorectal cancer screening. She had no prior colonoscopies. Two rectal polyps, measuring 5 mm and 15 mm, were identified during the procedure, along with internal hemorrhoids. Biopsies were obtained from both polyps. Histopathological examination revealed colonic mucosa infiltrated by sheets of lymphoid cells. Immunohistochemical staining demonstrated neoplastic B-cells positive for CD20 and BCL2. Scattered CD138+ plasma cells were also noted in the background. Furthermore, molecular studies detected clonal gene rearrangements involving the immunoglobulin heavy chain and kappa light chain genes. These findings were diagnostic of MALT lymphoma of the rectum. Discussion: This case highlights a rare presentation of rectal MALT lymphoma incidentally discovered during routine colorectal cancer screening in a patient without identifiable risk factors. GI lymphomas are uncommon, accounting for only about 4% of all GI neoplasms. Among these, the majority occur in the stomach, with primary rectal MALT lymphoma comprising less than 1% of cases. Given the rarity of primary rectal MALT lymphoma, this diagnosis emphasizes the importance of screening colonoscopies in the detection of common malignancies alongside atypical and rare pathologies. Management strategies for rectal MALT lymphoma vary and may include surgical resection, endoscopic mucosal resection (EMR), systemic chemotherapy, and radiation therapy. Early identification through routine screening can allow for timely intervention, even in asymptomatic patients.