Primary Diffuse Large B-cell Lymphoma of the Urinary Bladder: A Case Report and Narrative Review of Treatment Modalities and Clinical Outcomes.

Primary diffuse large B-cell lymphoma (DLBCL) of the urinary bladder is a rare extranodal lymphoma, representing a very small proportion of both bladder malignancies and extranodal lymphomas. We report a 73-year-old, chronically institutionalized woman with Eastern Cooperative Oncology Group (ECOG) 3-4 who presented with abdominal/flank pain, fever, hydronephrosis, and polymicrobial urosepsis. A bladder mass was detected incidentally on CT and subsequently confirmed by cystoscopy and transurethral resection of bladder tumor (TURBT). Histopathology showed a CD20-positive, CD5/CD10-negative large B-cell lymphoma (BCL) with Ki-67 of 50% (focally up to 80%), multiple myeloma oncogene (MUM)-1 positivity, and an isolated BCL6 rearrangement without concurrent myelocytomatosis oncogene (MYC) or BCL2 abnormalities, consistent with a high-grade, non-GCB DLBCL. Given her frailty and comorbidities, she was treated with rituximab monotherapy followed by involved-site radiotherapy instead of anthracycline-based chemoimmunotherapy, achieving marked metabolic and anatomic regression of the bladder lesion on positron emission tomography (PET)/CT. We present a narrative review of the literature on primary bladder DLBCL, highlight diagnostic and therapeutic considerations in the context of severe frailty, and discuss how de-escalated, organ-preserving strategies may be appropriate for selected patients.