High grade urothelial carcinoma in kidney transplant patients with a history of BK viremia – Just a coincidence?

Abstract Introduction Kidney transplant recipients (KTR) have a three‐to‐four‐fold increased risk of developing urothelial carcinoma (UC) compared to the general population. BK polyoma virus (BKV) infection is known to affect approximately 15% of KTR. In vitro models support a potential pathogenic role for BKV in the development of UC. We describe a series of UC in kidney transplant recipients. Methods Electronic patient records were searched to identify KTR with UC who had undergone kidney only or simultaneous kidney and pancreas transplantation in a single UK center between 2009 and 2015. Where available, stored pathological samples were retrieved, re‐examined and stained for SV40 as a marker of BKV using standard staining protocols for kidney biopsy samples. Results Fourteen KTR had developed UC post‐transplant. Of these, 10 KTR had a history of BKV infection post‐transplant. Six of these 10 KTR developed a rare micropapillary tumor subtype of UC which is typically only found in <1% of UC cases. All six micropapillary tumor samples stained positive for SV40, including samples from metastases. Three tumor samples were available from the four KTR with no history of BKV infection and were not micropapillary subtype and were negative for SV40. Three micropapillary tumors from immunocompetent patients were examined as controls and were negative for SV40. Conclusions These findings would support a pathogenic role for BK virus in the development of rare micropapillary subtype urothelial tumors in the kidney transplant population.