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Low-level BK polyomavirus (BKPyV) shedding is seen in at least 10% of seropositive immunocompetent adults. Moreover, BKPyV infection is highly prevalent amongst immunocompromised populations, yet little is known on its relationship with malignancy. We studied a female patient with BKPyV-associated and donor-derived high-grade sarcomatoid urothelial carcinoma developed 8 years after kidney transplantation from a male donor. Through whole-genome sequencing, we discovered integration of genotype IV BKPyV genome into the non-coding RNA (ncRNA) intronic region of human chromosome 18. The two breakpoints in the virus genome were located at the non-coding control region (NCCR) and large T antigen (TAg) coding region, respectively. Nevertheless, the TAg was overexpressed. We, therefore, inferred that the BKPyV was clonally integrated into the human genome in the form of concatemers, facilitating the expression of the TAg. The patient presented with multiorgan metastases, which were reduced in size and number throughout the body after removal of the graft and cessation of immunosuppressants. The few remaining lesions located in the liver were identified, through biopsy to be necrotic tumor tissue with TAg detected; additionally, genomic sequencing of the liver mass found Y chromosome. In conclusion, we propose that integration of the BKPyV genome is closely related to oncogenesis in this patient; while oncogenesis occurred when host immunity was impaired, recovery of the patient's native immunity effectively curbed viral replication and eliminated the metastatic lesions.

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