A renal oncocytoma is a benign epithelial cell tumor which comprises ~5% of all RCCs. As it is a benign epithelial tumor, there is an excellent prognosis.
Renal oncocytomas are often described as "brown tumors" with a sharp central stellate scar. Though this is characteristic of oncocytomas, it is only seen in 1/3 of cases. Further, renal cell carcinomas can also demonstrate a central scar.
Renal oncocytomas consist of large, acidophilic, mitochondria-rich tumor cells ("oncocytes") with granular cytoplasm and without perinuclear clearing. This is similar to chromophobic RCC, except that in renal oncocytoma there is no perinuclear halo with cells occurring as tumor nests (i.e. no perinuclear clearing).
This tumor arises from the intercalated cells of the tubular system. An oncocytoma is not confined to the kidneys and can develop in the thyroid, pancreas, and/or pituitary gland.
The classic triad of any RCC (including oncocytic RCC) consists of hematuria, flank pain, and a palpable flank mass. Painless or microscopic hematuria is the most common finding. It should be noted that only about 5-10% of patients present with this triad and greater than 25% present with 1+ atypical symptoms usually related to paraneoplastic syndromes and/or disseminated disease.
Flank pain can occur in later stages and correlates to larger tumors.
If the tumor grows to a sufficient size, it may be palpable during an abdominal examination.
Renal oncocytomas are not invasive but are capable of transforming into a malignant oncocytic RCC.
Though benign, renal oncocytomas are often surgically resected (especially if tumor increases in size), as they may transform into a malignant oncocytic RCC.
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