Tubulocystic carcinoma of the kidney: a new entity among renal tumors.

Tubulocystic carcinoma is a tumor entity, which is not yet included in the WHO-classification of renal tumors. We report a series of 11 cases of this tumor, 6 of which were examined in by immunohistochemistry using a panel of five antibodies (CK7, CK34betaE12, CK19, CD10 and P504S). All patients were men. Each had renal tumor stage of pT1N0M0, with a diameter of 1.7 to 7 cm (mean, 3.3 cm). None of the patients presented with recurrence or metastases. Grossly, tumors were microcystic masses with a bubble-wrap appearance. Histological features included cysts and small tubules, separated by delicate septa and lined by flat to columnar or hobnail cells. The cyst and tubule epithelium showed immunohistochemical characteristics of both proximal and distal tubules. Tubulocystic carcinoma is a distinctive kidney tumor, with noteworthy macroscopic and microscopic characteristics, which can be distinguished from other cystic kidney tumors, including cystic nephroma, multilocular cystic renal cell carcinoma and some solid tumors with extensive cystic changes. More cases are needed to ascertain its prognosis. Tubulocystic carcinoma should be considered as a new subtype of renal cell carcinoma in the next revision of the WHO classification.