DOI: https://doi.org/10.36347/sasjm.2026.v12i02.004

Pages: 102-104

Primary rectal lymphoma is an exceptionally rare form of extranodal non-Hodgkin lymphoma with nonspecific clinical manifestations, often leading to delayed diagnosis. We report the case of a 75-year-old patient presenting with progressive asthenia, chronic diarrhea, abdominal pain, significant weight loss, and nocturnal fever. Clinical examination revealed peripheral lymphadenopathy without hepatosplenomegaly. Computed tomography demonstrated circumferential rectosigmoid wall thickening associated with multiple abdominopelvic and inguinal lymphadenopathies. Rectosigmoidoscopy identified an ulcerative-proliferative circumferential rectosigmoid lesion, and histopathological examination of biopsies showed diffuse large atypical lymphoid cell proliferation. Immunohistochemistry revealed strong CD20 and BCL6 expression, absence of MUM1 expression, and a high Ki-67 proliferation index, consistent with germinal center-type diffuse large B-cell lymphoma according to the 2022 WHO classification. The patient was managed with systemic immunochemotherapy using the R-CHOP regimen, with a favorable initial response. This case highlights the diagnostic challenges posed by primary rectal lymphoma due to its rarity and nonspecific presentation, as well as the essential role of histopathology and immunophenotyping in establishing the diagnosis. Reporting such cases contributes to improving awareness, diagnostic accuracy, and therapeutic decision-making for this uncommon but aggressive malignancy.