Primary Colonic Diffuse Large B-cell Lymphoma: A Diagnostic Challenge.

Primary colonic diffuse large B-cell lymphoma (DLBCL) is a rare extranodal malignancy that accounts for a small percentage of colonic malignancies. With nonspecific gastrointestinal symptoms such as weight loss, abdominal pain, and bloody stools, it may mimic the presentation of inflammatory bowel disease. Symptoms usually present in advanced stages of the disease. We present the case of a 19-year-old man with a history of one year of intermittent abdominal pain, unintentional weight loss, diarrhea, and bloody stools. Initial abdominal ultrasound reported distended bowel loops with no evidence of masses. During hospitalization, the patient underwent a colonoscopy, which revealed a transmural exophytic mass in the cecum near the ileocecal valve. A biopsy was taken, and findings suggested chronic inflammatory colitis. The patient was treated initially with corticosteroids and subsequently discharged with oral prednisone. However, four weeks later, the patient presented with persistent symptoms and recurrent episodes of bloody stools, which prompted admission and a second colonoscopy. During his admission, progressive intestinal obstruction prompted a right hemicolectomy. Histopathological examination of the surgical specimen revealed DLBCL with CD20 positivity on immunohistochemistry, establishing the diagnosis of primary colonic lymphoma. This case highlights the diagnostic challenge posed by primary colonic DLBCL in young patients and emphasizes the importance of clinical suspicion and maintaining a broad differential diagnosis when histopathological findings are inconclusive.