Unusual BK polyomavirus-associated urologic malignancies in renal transplant recipients: Report of two cases and review of the literature.

Renal transplant recipients are at increased risk of developing urologic malignancies, some of which are associated with prolonged BK virus infection. We report two cases of BK virus-associated carcinoma with variant morphological patterns (clear cell adenocarcinoma of the bladder and micropapillary urothelial carcinoma of the pelvicaliceal system) arising in the urinary tract of renal transplant recipients. In both cases, the diagnosis was initially established on cytologic specimens: on urine cytology in one patient and on fine needle aspiration of an inguinal lymph node in the other patient. The unusual cytologic features of both cases (multiple morphologies in one patient and micropapillary pattern in the other), co-occurrence of decoy cells in the urine of one patient and the occurrence of these tumors in renal transplant recipients raised the possibility of BK polyomavirus-associated malignancy and led to confirmatory SV40 immunostains that were positive. These cases expand the morphologic variants of BK virus-associated urologic malignancies diagnosed in solid organ transplant patients. While differentiating BK virus-infected cells from malignant cells in urine cytology specimens is a diagnostic challenge, greater awareness of their possible co-existence is vital, as this could be the only chance for an early diagnosis.