Objective    To study the clinicopathologic

immunohistochemical features and differential diagnosis of metanephric adenoma (MA).     Methods    Two cases of MA recently diagnosed in our institute were observed and analyzed in the gross

histologically and immunohistochemically. Pathological features were concluded based on clinical information extracted from the medical records and literature review.     Results    Both tumors were masses of round in shape

gray-white in color

and 1 or 4 cm in size

enveloped with a thin capsule with a clear boundary in macroscopic view. They also had distinct feature in histology as small cells with high ratio of nucleus to cytoplasm

no nuclear atypia or mitotic figures. The tumor exhibited well-organized tubules

small cell nests

‘glomeruloid bodies’

and sharply demarcated from the adjacent renal parenchyma. Immunohistochemical phenotype of expression profiles were as diffused vimentin

diffused or partially positive WT1

focalized CK

spotty or small focal of CD57 in one case while strong patchy expression in another case. The expression of EMA

CK7

CgA

CD10 were negative. Both cases were middle to old-aged females. In one case there was renal cell carcinoma located elsewhere in the same kidney.     Conclusion    MA

a rare novel form of benign renal neoplasma in the WHO classification

has distinct architecture in tissue structure. MA has characteristic phenotypes

as consistent expression of vimentin and frequent expressions of WT1

CD57

and CK

which are various in both intensity and distribution

but EMA

CK7

CgA

CD10 are negative. So far

it is believed to a benign tumor and should be differentiated from Wilms tumor

papillary renal cell carcinoma (PRCC)

metanephric adenofibroma etc.