Q 16. A 62 year-old immunocompromised male developed hematuria 15 years after heart transplantation.

A 62-year-old immunocompromised man developed hematuria 15 years after heart transplantation. He had a history of groin squamous cell carcinoma in situ of the skin. A midstream voided urine was submitted for evaluation. Urine cytology demonstrates squamous cell carcinoma, but the concurrent cystoscopic bladder biopsy is negative.  Which explanation is most appropriate?