ABSTRACT
<p><b>OBJECTIVE</b>To investigate the clinicopathological characteristics and the diagnosis of multilocular cystic renal cell carcinoma (MCRCC).</p><p><b>METHODS</b>The clinicopathological data of 19 MCRCC cases were collected and immunohistochemical staining assays were carried out. Forty-six cases of other cystic kidney lesions within the same period were collected as controls, including extensively cystic clear cell RCC (12 cases), clear cell tubulopapillary renal cell carcinoma (6 cases), tubulocystic carcinoma (2 cases), simple cortical cysts (22 cases), multilocular cystic nephroma (1 cases) and multicystic kidney (3 cases).</p><p><b>RESULTS</b>The patients included 14 males and 5 females. The ages ranged from 31 to 66 years (median age = 50 years). Most of the MCRCC cases were detected incidentally in physical examination, occasionally accompanied with hematuria, back pain or other symptoms. The follow-up period of 17 patients ranged from 6 to 170 months. All patients were alive without evidence of tumor recurrence or metastasis. Pathological findings showed that macroscopically, tumor size ranges from 1.5 to 7.0 cm in the maximum diameter, generally a entirely of various sized. The cysts contain serous, hemorrhagic or turbid fluid. Solid areas or substantially discernible mural nodules were absent; histologicallly, single layer of cuboidal and flattened epithelial tumor cells were lined in the cysts, described as clear cytoplasm, small nuclear, no nucleoli and low Fuhrman nuclear grade (I or II). Multilayer tumor cells could be observed in a few cysts, with granular cytoplasm and small intracystic papillae formed. The clear tumor cell clusters, similar as cystic lined tumor cells, were seen within pathological fibrous in almost all cases, and significant myofibroblastic proliferation was found in 14 cases. Immunohistochemically, the cysts lined epithelial cells and the clear tumor cell clusters were positive for epithelium markers, including CKpan(19/19), EMA(16/19) and CK7 (15/19); higher percentage of CAIX (17/19) and PAX8(15/19) than control groups, but lower percentage of CD10 (7/19), RCC (6/19) and AMACR(2/19); and all were negative for 34βE12, CD117 and CD68.</p><p><b>CONCLUSIONS</b>Multilocular cysts, clear cells clusters of low Fuhrman grade within fibrous septa and capillary vessel proliferation under epithelium are important features of MCRCC. The united using of CAIX, CK7, CD10 and RCC is helpful for differentiating variable cystic renal tumor. MCRCC usually has an excellent prognosis, nephron sparing surgery is first recommended as a therapeutic strategy.</p>