Atypical Presentation of Diffuse Large B-Cell Lymphoma of the Caecum in a Young Patient: A Case Report.

Primary diffuse large B-cell lymphoma (DLBCL) of the colon, particularly involving the caecum, is rare and often poses a diagnostic challenge due to its non-specific presentation and the low incidence of colorectal involvement. Early recognition is crucial, as timely diagnosis and multidisciplinary management can significantly improve patient outcomes. A 29-year-old female presented with a two-week history of intermittent lower abdominal pain, progressive abdominal bloating, weight loss, night sweats, and bilateral ankle swelling over the last four weeks. Initial ultrasonography revealed a large soft tissue mass within the abdomen, initially reported as an ovarian mass; however, further evaluation, including CT imaging and colonoscopy, revealed an ulcerated, partially obstructing caecal mass. Histopathological examination of endoscopic biopsies confirmed DLBCL, non-germinal-centre B-cell subtype. PET imaging revealed multiple large, intensely fluorodeoxyglucose (FDG)-avid lymph nodes below the diaphragm forming a bulky nodal mass, along with a similarly FDG-avid caecal mass, strongly suggesting extra-nodal lymphoma involvement. The patient was subsequently managed with R-CHOP (rituximab, cyclophosphamide, doxorubicin hydrochloride (hydroxydaunorubicin), vincristine sulfate (Oncovin), and prednisone) chemotherapy under the guidance of a multidisciplinary team. Primary colonic DLBCL is rare, accounting for a small fraction of colorectal malignancies. Its non-specific symptoms, including abdominal pain, altered bowel habits, and constitutional complaints, can mimic more common gastrointestinal conditions. This case highlights the importance of maintaining a broad differential diagnosis, especially in younger patients. While imaging modalities, endoscopic assessment, and histopathology are critical for accurate diagnosis, prompt oncologic consultation and chemotherapy remain central to management. A multidisciplinary treatment approach is vital in improving patient prognosis.