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Background BK virus-induced nephropathy in renal transplantation is well recognized but its oncogenic potential is less appreciated. Methods We report a case of high-grade urothelial tumor in a renal transplant recipient with chronic BK viremia in the absence of BK nephropathy successfully treated with intravesical Bacillus Calmette-Guerin (BCG) instillation. Following BCG therapy, there was also spontaneous clearance of BK viremia. Results In July 2011, Mr. LYY, a 57-year-old Chinese man with end-stage renal failure secondary to chronic glomerulonephritis underwent uncomplicated deceased donor renal transplantation. One year later, he developed persistent high-level BK viremia despite reduction in immunosuppression. He was also treated with a course of ciprofloxacin from January to October 2013, and intravenous immunoglobulin (IVIG) in February 2013, but high-level BK viremia persisted. In spite of this, his graft function was preserved. He was subsequently placed on BK surveillance alone. Chronic BK viremia persisted for the next 5 years with stable graft function. See Figure 1. In February 2018, an incidental urinary bladder nodule was picked up on computed tomography (CT) scan performed for evaluation of urosepsis. Follow-up flexible cystoscopy in May 2018 showed a 1.5 cm papillary tumor over the left superior bladder wall. Transurethral resection of bladder tumor (TURBT) was performed and histopathological examination revealed high-grade papillary urothelial carcinoma. In addition, the biopsy specimen was stained positive for SV40, suggesting the possible association between chronic BK virus replication in the bladder and oncogenesis. Relook TURBT in July 2018 revealed a persistent erythematous patch over the posterior bladder wall. Given the cystoscopic findings, Mr. LYY received a weekly instillation of intravesical BCG for 6 weeks. He tolerated the intravesical BCG treatment with no local or systemic complications. Interestingly, his serum BK viral loads dropped below lower limits of detection thereafter and continued to remain so for the next 4 months. Conclusion We postulate that the intravesical BCG therapy triggered an immune response that targeted not only the tumor but also the BK virus infection, resulting in successful clearance of chronic BK viremia. Disclosures All authors: No reported disclosures. [ABSTRACT FROM AUTHOR]