BK Polyomavirus-Associated Carcinoma In Situ of the Renal Allograft: Balancing Oncologic Control and Graft...

Renal transplant recipients are at increased risk of urothelial carcinoma (UC), with BK polyomavirus (BKPyV) increasingly implicated as a potential oncogenic driver in immunosuppressed patients. BKPyV-associated UC is rare, and carcinoma in situ (CIS) involving the renal allograft is exceptionally uncommon. Management is particularly challenging, as treatment must balance oncologic control against preservation of graft function and avoidance of return to dialysis, with limited evidence available to guide kidney-sparing approaches.

We present a case and updated literature review of BKPyV-associated urothelial CIS arising within a renal allograft in a female renal transplant recipient in her 60s with prior BKPyV nephropathy. Clinical, cytologic, radiologic, and histopathologic findings were reviewed alongside relevant literature describing BKPyV-associated urothelial malignancies in transplant recipients. Histopathology demonstrated high-grade atypia with diffuse SV40 and p53 positivity, supporting viral-associated oncogenesis.

The patient presented with biopsy-proven urothelial CIS involving the renal medulla without visible upper tract lesions on imaging or endoscopy. Owing to the morbidity associated with radical urothelial clearance and the patient's desire to preserve graft function and avoid dialysis, a kidney-sparing approach using intrarenal gemcitabine instillation and intensive surveillance was undertaken. Initial surveillance demonstrated negative upper tract washings and no radiologic progression; however, a repeat transplant biopsy 2 years later demonstrated persistent CIS with ongoing BKPyV replication. A literature review identified more than 40 reported cases of BKPyV-associated UC in immunosuppressed patients, the majority demonstrating aggressive histologic features and poor oncologic outcomes.

BKPyV-associated urothelial CIS of the renal allograft is an exceptionally rare but clinically significant entity. Management remains challenging, requiring a careful balance between oncologic control and allograft preservation. This case demonstrates a pragmatic kidney-sparing treatment strategy using localized therapy and close surveillance, although persistent disease remains a concern. Further research is required to guide the optimal management of BKPyV-associated urothelial malignancy in transplant recipients. This case is particularly relevant to the Australian transplant population given the high burden of renal transplantation, increasing long-term graft survival, and the growing recognition of BKPyV-associated malignancy in chronically immunosuppressed patients, for whom management decisions may directly impact graft preservation and dialysis dependence.