An Unexpected Surge in Plasma BKPyV Viral Load Heralds the Development of BKPyV‐Associated Metastatic Bladder Cancer in a Lung Transplant Recipient With BKPyV Nephropathy

We report a lung transplant recipient who developed BK polyoma virus (BKPyV) DNAemia and BKPyV nephropathy. With careful management of his immunosuppression he achieved significant reduction in BKPyV DNAemia and stabilization of his kidney function. He later developed a high‐grade bladder cancer and shortly thereafter he experienced a major upsurge in the level of BKPyV DNAemia that coincided with the discovery of hepatic metastasis. Retrospectively, the bladder cancer and the hepatic secondary tumor stained uniformly for SV40 large T antigen, and the BKPyV DNA sequences identified in plasma corresponded to BKPyV DNA within hepatic tissue, indicating that the spike in BKPyV load was likely derived from the circulating tumor cells or cell‐free tumor DNA following metastases of a BKV‐associated cancer. To the best of our knowledge, this is the first description of a surge in BKPyV load in a patient with controlled BKPyVN that heralded the appearance of a metastatic urothelial malignancy. This report discusses the literature on BKPyV‐associated malignancies and the possibility that unexplained increases in BKPyV DNAemia may be a biomarker for metastatic BKPyV‐related urothelial cancer. This report describes a lung transplant recipient with quiescent BK polyoma nephropathy who developed a BK polyoma–driven urothelial cancer with widespread metastasis and a surge in plasma BK polyoma viral load, likely originating from integrated BK polyoma DNA sequences in metastatic tumor cells.