ABSTRACT
<p><b>OBJECTIVE</b>To investigate clinicopathological features and differential diagnosis of tubulocystic carcinoma of the kidney.</p><p><b>METHODS</b>The clinical features, histological and immunohistochemical findings were analyzed in 3 cases of tubulocystic carcinoma of the kidney, along with review of the related literatures.</p><p><b>RESULTS</b>Three patients were males with a mean age of 59 years old (range from 44 to 71 years). All presented with no symptom and their tumors were found during routine examination. The tumor size ranged from 1.5 to 5.0 cm in greatest dimension. The tumors were grossly well-circumscribed without capsules and exhibited a spongy cut surface. Microscopically, all three tumors were composed of tubules and cysts of varying sizes separated by thin fibrous septa. The epithelial lining cells were flat, cuboidal and columnar, with often a hobnail-like appearance characterized by abundant eosinophilic cytoplasm with prominent nucleoli. Two cases showed focal clear cytoplasm. One of the three cases coexisted with a papillary renal cell carcinoma. Immunohistochemically, all 3 cases showed positivity for pan-CK, vimentin, CK19, CD10, P504S, and focal positivity for 34βE12. Two cases showed focal positivity for CK7.</p><p><b>CONCLUSIONS</b>Tubulocystic carcinoma of the kidney is a rare kidney neoplasm and occurs predominantly in males. The tumor is characterized by gross spongy appearance and microscopic cysts and tubules often lined by hobnail-like cells and separated by thin fibrotic stroma. The differential diagnosis mainly includes other lesions of the kidney that have a multicystic growth pattern.</p>