Micropapillary urothelial carcinoma: an aggressive variant of urothelial carcinoma.

: Micropapillary urothelial carcinoma (MPC) is a rare variant of urothelial carcinoma (UC) with an aggressive clinical course, an advanced stage at first presentation and a high metastatic potential. The aim or our study is to present five illustrative cases of MPC, diagnosed among the 21 patients with UC treated by radical cystectomy in the Department of Urology, County Hospital of Tirgu Mures, Romania, between January 1, 2011 and December 31, 2013. The morphological and immunohistochemical features of this rare and aggressive variant of UC, as well as a brief review of the literature are all presented. All five cases were associated with lymph node metastases with micropapillary features, regardless of the microscopic aspect of the tumor on the surgical specimens [transurethral resection (TUR) or cystectomy]. Three of them had a micropapillary component in the TUR, on the cystectomy specimen, or in both, along with lymph nodes metastases. In two cases, the MPC features were present only in the lymph node metastasis, with a conventional UC on the TUR and on the cystectomy. Immunohistochemical staining demonstrated that both micropapillary and associated conventional UC were positive for CK7 and CK20. Ki67 was expressed in 40% of tumor cells and CD34 was positive in the endothelial cells and negative in the flattened spindled cells lining the retraction spaces around tumor cell nests. MPC is a highly aggressive variant of UC with specific morphological characteristics. Any amount of micropapillary component found in UC is significant, and should be reported because it encompasses an aggressive clinical behavior and a poor prognosis.