Distinguishing between oncocytoma and the eosinophilic variant of chromophobe renal cell carcinoma is a significant and relatively frequent problem for surgical pathologists. This is my experience of just such a case.
Macroscopically radical nephrectomy showed a well circumscribed upper pole tumour with a firm homogenous tan/brown appearance upto 40mm. There was no evidence of cystic change or necrosis. Typically both chromophobe and oncocytoma have a similar appearance as described above – a well circumscribed tumour with homogenous tan/brown appearance whilst a oncytoma may also show a central stellate scar.
On microscopy chromophobe characteristically shows large polygonal cells with prominent cell membranes (with an embossed appearance), Nuclei are small with a wrinkled appearance and there is often a prominent perinuclear halo. Oncocytomas characteristically show solid compact nests, acini, tubules or microcysts of oncocytes which are large polygonal cells with dense eosinophilic cytoplasm round and regular round nuclei.
Histologically my case showed features of both with architecturally areas showing nests and acini typical of oncocytoma however more solid areas with large polygonal cells with prominent cell membranes however lacking perinuclear halos and a small wrinkled appearance.
Immunohistochemistry for distinguishing conventional RCC, chromophobe and oncocytoma:
RCC, CD10 and Vimentin are positive and CD117 neg and E-cadherin neg in conventional RCC, compared to chromophobe & oncocytoma which tend to be positive for CD117 and e-cadherin.
CK7 is useful in the distinction of chromophobe/oncocytoma with chromophobe tending to show a more diffuse positivity whilst with oncocytoma a patchy staining.
CD15 is thought to be positive in oncocytoma and neg in chromophobe. And oncocytoma tends to show stronger staining with ecadherin than chromophobe.
This case showed positivity to CD117, ecadherin and CD15 and negativity to vimentin and CK7 favouring a diagnosis of oncocytoma.
Prognosis: Oncocytoma is thought to be an entirely benign entity. Chromophobe renal cell carcinoma has been shown to have a significantly better prognosis than conventional renal cell carcinoma.
Boswick. Urologic Surgical Pathology
WHO classification of tumours: Tumorus of the Urinary System and Male Genital Tract.