Tubulocystic carcinoma of the kidney

Tubulocystic carcinoma is a rare renal tumor with distinct characteristics which were recently described in 3 large series (Amin et al, Am J Surg Pathol. 2009;33:384-392; Azoulay et al, Virchows Arch. 2007;451:905-909; Yang et al, Am J Surg Pathol. 2008;32:177-187). These well-circumscribed tumors are usually solitary and are composed of closely packed tubules and cysts separated by fibrous stroma and lined by a single layer of cuboidal cells with eosinophilic cytoplasm and prominent nucleoli, sometimes with a hobnail appearance. These tumors show a low but definite risk of metastasis, and it is therefore important to distinguish them from other benign and malignant renal lesions included in the differential diagnosis.Although originally described as a low-grade collecting duct carcinoma, the current morphologic features, immunohistochemical profile, and molecular signature of this tumor do not support its origin from the collecting ducts of Bellini. The current literature is reviewed in this article, and evidence is presented that tubulocystic carcinoma is a distinct renal epithelial neoplasm, with a possible relationship to papillary renal cell carcinoma.