Polyomavirus (BK)-associated pleomorphic giant cell carcinoma of the urinary bladder: a case report

This report describes the morphological features of a pleomorphic giant cell carcinoma with focal trophoblastic differentiation of the urinary bladder in a male, 12 years post living related donor renal transplant. The voided urine cytology demonstrated rare decoy cells admixed with markedly atypical urothelial cell clusters, papillae and giant cells. Cystoprostatectomy demonstrated a nodular mass involving the trigone and right lateral-posterior wall, adjacent to the ureteral orifice. Hematoxylin-eosin stained sections showed two synchronous malignancies: (a) pleomorphic giant cell carcinoma with focal trophoblastic differentiation of the urinary bladder, metastatic to the omentum and (b) prostatic adenocarcinoma, Gleason score 3 + 4 = 7, involving the right prostate lobe. Strong diffuse expression of polyomavirus large T antigen was demonstrated in the primary and metastatic pleomorphic giant cell carcinoma, supporting a possible role for polyomavirus (BK) in the oncogenetic pathway. The prostatic adenocarcinoma was negative for polyomavirus large T antigen. Our findings of p63, CK7 and CK903 expression in pleomorphic giant cell carcinoma suggest that the tumor is of urothelial derivation. This is the first report describing the morphological features of urinary bladder pleomorphic giant cell carcinoma with trophoblastic differentiation, positive for polyomavirus large T antigen, arising in the background of BKV reactivation.