The nested variant of transitional cell carcinoma: an aggressive neoplasm with innocuous histology.

The nested variant of transitional cell carcinoma (TCC-NV) is a rare neoplasm; only eight cases have been described. This report reviews the clinicopathologic features of 16 additional examples. The cases were collected from consultations received during a 13-year period. In most instances, a consultation was sought because the histologic features suggested an atypical proliferation of Brunn's nests or a lesion similar to the previously published examples of TCC-NV. Clinical data were gathered and tissues were studied to exclude prostatic cancer and adenocarcinoma. TCC-NV is characterized by the presence of irregular nests and/or tubules of transitional cells infiltrating the lamina propria without surface involvement. Neoplastic cells tend to have innocuous features but at least a few cells in every case are cytologically anaplastic. There is a marked male predominance. Synchronous or metachronous TCCs of more usual histologic make-up may occur. After a follow-up averaging 16.6 months, only three patients are known to be alive with no evidence of disease. Clinicopathologic information from our 16 cases combined with the 8 previously reported examples confirms that TCC-NV is a persistent and aggressive neoplasm notable for its innocuous appearance in histologic preparations.