Primary Ureteric Diffuse Large B‐Cell Lymphoma (Non‐GCB Subtype) Presenting as Obstructive Uropathy: A Rare Case Report

Background Primary ureteric lymphoma is an exceptionally rare extranodal manifestation of non‐Hodgkin lymphoma and often mimics more common ureteric malignancies. Diffuse large B‐cell lymphoma (DLBCL), particularly the nongerminal center B‐cell (non‐GCB) subtype with triple‐expressor phenotype, is associated with aggressive biological behavior and poorer prognosis. Case Presentation A 60‐year‐old female presented with right‐sided flank pain, oliguria, and intermittent vomiting for 8 days. Clinical evaluation revealed bilateral hydronephrosis, and imaging demonstrated periureteric soft‐tissue masses encasing the distal ureters and pelvic vessels, causing obstructive uropathy. Differential diagnoses included urothelial carcinoma and lymphoma. CT‐guided ureteric biopsy showed diffuse infiltration by atypical lymphoid cells positive for CD45, CD20, CD30, MUM1, PAX5, BCL6, c‐MYC (45%), and BCL2, with a high Ki‐67 index (~98%). The tumor cells were negative for CD10, cytokeratin, and GATA3, confirming DLBCL, non‐GCB subtype, with a triple‐expressor phenotype. PET‐CT staging showed disease confined to the ureteric segments, with no systemic nodal or extranodal involvement, supporting a primary ureteric origin. Bilateral double‐J stenting was performed to relieve obstruction and stabilize renal function, followed by six cycles of R‐CHOP chemoimmunotherapy. The patient demonstrated marked clinical and biochemical improvement, with normalization of renal function and no evidence of recurrence at 6 months of follow‐up. Conclusion This case highlights the importance of considering primary ureteric lymphoma in the differential diagnosis of atypical ureteric masses, especially with bilateral involvement. Early histopathological confirmation and prompt initiation of systemic therapy can result in favorable outcomes, even in aggressive molecular subtypes. Multidisciplinary evaluation and timely decompression are essential to optimize renal recovery and treatment tolerance.