BK virus nephropathy, collecting duct cell proliferation and malignancy in a renal allograft: Case history and review of the literature

We report an anti-SV40 positive collecting duct (CD) cell carcinoma in a renal allograft 4.5. years after transplantation that developed during smoldering BK virus (BKV) nephropathy. In the allograft biopsy six months after transplantation documenting BK nephropathy, anti-SV40 positivity co-localized with the CD marker CK-HMW and proliferation marker MIB-1, suggesting that BKV preferentially infects CD cells and causes them to proliferate. In previous reports on BKV related renal malignancies, immunohistochemistry also pointed to a CD origin of the tumors. Six additional cases of BKV induced renal tumors were found in four CD carcinoma case-reports and one large case-series of "usual" CD carcinomas, supporting the hypothesis that BKV specifically induce CD cell tumor formation. In view of the rarity of BKV induced tumors a second hit might be needed to induce malignancy. In our case the use of lithium-which also causes CD cell proliferation-at the time of BKV infection may have provided this second hit.