Flow cytometry of renal oncocytoma: common occurrence of deoxyribonucleic acid polyploidy and aneuploidy.

Flow cytometry was performed on 51 typical specimens of renal oncocytoma. Nuclei were extracted from paraffin-embedded archival material and isolated nuclei were stained with propidium iodide. Of the 51 available tissue blocks 86 per cent were evaluable and 50 per cent of these samples showed a deoxyribonucleic acid (DNA) histogram that was approximately the same as normal renal parenchyma. Of the oncocytoma samples 39 per cent showed a marked increase (more than 10 per cent of the nuclei) in the tetraploid DNA peak, while 11 per cent showed a distinct DNA aneuploid peak. Among 21 evaluable grade 2 oncocytic renal tumors 33 per cent showed a normal DNA histogram, 43 per cent showed a marked increase in the DNA tetraploid peak and 24 per cent showed a DNA aneuploid peak. The common presence of polyploid nuclei containing double quantities of chromosomal DNA may correlate with the long-standing pathological observation that oncocytic tumors often contain a distinct population of large nuclei. Indeed, 86 per cent concurrence was seen between the detection of an abnormal DNA content by flow cytometry and the histopathological presence of large abnormal nuclei in these specimens. Since renal oncocytomas (grade 1 oncocytic tumors) rarely, if ever, metastasize and are relatively noninvasive locally, their markedly abnormal flow cytometry patterns are of considerable interest. Moreover, DNA polyploidy has not been identified previously in renal tumors. The biological significance and mechanism of DNA polyploidy, and the relationship of DNA polyploidy and DNA aneuploidy to the pathogenesis of oncocytic renal tumors require further laboratory investigation. The clinical use of flow cytometry to classify and to predict the behavior of renal tumors will be complicated, since renal oncocytomas commonly have polyploid and aneuploid DNA histograms.