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Invasion of Renal Parenchyma: Although grossly demarcated from the kidney, clear cell sarcoma of kidney (CCSK) frequently infiltrates into the adjacent renal parenchyma, entrapping tubules of medulla and occasional glomeruli, like in mesoblastic nephroma.
The entrapped tubules may undergo metaplasia and appear embryonal, mimicking neoplastic tubules of Wilms tumor. However, Wilms tumor shows more aggressive infiltration of the kidney with entrapment of entire chunks of renal parenchyma as opposed to single tubules entrapped by CCSK. Some of the entrapped tubules undergo cystic change to form grossly evident cysts, simulating cystic nephroma.
The entrapped tubules may undergo metaplasia and appear embryonal, mimicking neoplastic tubules of Wilms tumor. However, Wilms tumor shows more aggressive infiltration of the kidney with entrapment of entire chunks of renal parenchyma as opposed to single tubules entrapped by CCSK. Some of the entrapped tubules undergo cystic change to form grossly evident cysts, simulating cystic nephroma.