Abstract
BACKGROUND: Urothelial bladder carcinoma is extremely rare in children and its association with BK virus infection remains unclear. METHODS: We describe the case of an 11-year-old girl who developed a urothelial carcinoma of the bladder four years after receiving her first kidney transplant. Kidney failure was secondary to nephronophthisis (NPHP6 variant), diagnosed in the neonatal period and associated with Leber congenital amaurosis and intellectual disability. She underwent peritoneal dialysis for four years before kidney transplantation at 6.5 years of age. Five months post-transplant, she developed BK virus-associated nephropathy, leading to chronic allograft dysfunction. Four years later, a routine ultrasound revealed an asymptomatic bladder mass without evidence of extension. The lesion was resected endoscopically and later managed with partial cystectomy. RESULTS: Histopathologic analysis confirmed a high-grade invasive urothelial carcinoma (pT2). Immunohistochemistry showed SV40 positivity, consistent with BK virus-induced neoplasia, while non-tumoral cells were negative. BK viremia had been undetectable one year prior to diagnosis. The patient remained disease-free for seven years following surgery, without adjuvant therapy. CONCLUSION: The involvement of BK virus in the development of bladder cancer has not yet been clarified. This case supports a possible role of BK virus in urothelial tumorigenesis, particularly in immunosuppressed transplant recipients.