An oncocytoma is a tumor made up of oncocytes, which are a special kind of cells. more...
This is an epithelial tumor composed of large, eosinophilic cells having small, round, benign-appearing nuclei that have large nucleoli. It is thought to arise from the intercalated cells of collecting ducts. It is not an uncommon tumor, accounting for approximately 5% to 15% of surgically resected renal neoplasms. Ultrastructurally, the eosinophilic cells have numerous mitochondria. In gross appearance, the tumors are tan or mahogany brown, relatively homogeneous, and usually well encapsulated. However, they may achieve a large size (up to 12 cm in diameter). Although anecdotal cases with metastases have been reported, the tumor is considered benign. There are some familial cases in which these tumors are multicentric rather than solitary.
from: Robbins pathology ,page 1015
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