Colitis or Cancer? A Rare Case of Colonic MALT Lymphoma Revealed Through Biopsy

Abstract

Colonic mucosa-associated lymphoid tissue (MALT) lymphoma is an uncommon subtype of extranodal marginal zone non‑Hodgkin lymphoma that may clinically and endoscopically mimic inflammatory bowel disease (IBD), leading to significant diagnostic delays. Although gastric MALT lymphoma is well characterized, colonic involvement is rare and accounts for only a small proportion of cases worldwide. We present an expanded case of a 77‑year‑old male who presented with chronic diarrhea, profound weight loss, and colonic inflammation initially misinterpreted as ulcerative colitis. Histopathologic evaluation ultimately demonstrated a monoclonal lambda‑restricted B‑cell infiltrate consistent with low‑grade MALT lymphoma. Staging with PET/CT revealed widespread low‑grade lymphadenopathy consistent with Ann Arbor Stage III disease. This report underscores the importance of thorough diagnostic evaluation when endoscopic findings resemble IBD, particularly in older adults, and highlights current evidence-based approaches to diagnosis, staging, and management of colonic MALT lymphoma