Review of tubulocystic carcinoma of the kidney with focus on clinical and pathobiological aspects.

Tubulocystic carcinoma of the kidney (TCK) is a recently established entity in renal neoplastic pathology. This review aims to give an overview of the clinical and pathobiological aspects of TCK. Grossly, the TCKs are well-demarcated multicystic lesions giving a "wrapped bubble" or "spongy" appearance. Microscopically, the tumors are composed of multiple, variably sized cysts separated by thin fibrous septa lacking ovarian stroma or desmoplastic reaction. The cysts are lined by tumor cells with eosinophilic cytoplasm and nuclear atypia of variable, but not infrequently of high grade corresponding to Fuhrman grade 3. A frequent association with papillary tumors has been reported. Recent molecular genetic studies of TCK have revealed distinct features separating this subset of renal cell carcinomas (RCCs) from other types of renal tumors including collecting duct carcinoma of Bellini and renal medullary carcinoma as well as pointing towards a close kinship with papillary RCC. Tubulocystic carcinoma of the kidney generally pursues an indolent clinical course. However, several cases with aggressive clinical behavior have been reported. We strongly feel that there is enough clinicopathological evidence to corroborate TCK as a separate entity and that it should be incorporated into the next WHO classification of renal tumors as a separate neoplastic category.