The nested variant of urothelial carcinoma: an aggressive tumor closely simulating benign lesions.

The "nested" variant is a rare form of urothelial carcinoma and its biologic behavior is highly aggressive. Herein two new cases of nested variant of urothelial carcinoma with immunohistochemical examination are presented. In one of the cases, the tumor extended through the bladder wall into the perivesicular soft tissue, prostatic urethra and left vesicula seminalis, and metastasized to obturator lymph nodes. In the other case, invasion of muscular layer was observed and three recurrences were developed during a follow-up period of 23 months. Both tumors of our study demonstrated high p53 and Ki-67 indices, supporting the aggressive nature of such tumors.