Eosinophilic renal cell tumours. A study on tumour heterogeneity with special emphasis on oncocytes

Eosinophilic renal tumour cells are found in oncocytomas, granular cell carcinomas, clear cell carcinomas and in a recently defined entity known as "congeners of oncocytomas". Ultrastructural examination of paraffin embedded tumour tissue representing eosinophilic areas in 40 renal cell tumours was performed in order to characterize the different types of eosinophilic cells. The results showed all tumours diagnosed light microscopically as oncocytomas to be composed of cells containing abundant mitochondria. Similar cells were, however, also found in one case of a clear cell carcinoma and in one case diagnosed light microscopically as a "congener". Oncocytes may therefore be found as part of non-oncocytomas and there seems to be a gradual transition from oncocytes to other eosinophilic cells of renal cell carcinomas. Preoperative subclassification of renal cell tumours based on small biopsy specimens is thus of limited value.