Eosinophilic and classic chromophobe renal cell carcinomas have similar frequent losses of multiple chromosomes from among chromosomes 1, 2, 6, 10, and 17, and this pattern of genetic abnormality is not present in renal oncocytoma.

That chromophobe renal cell carcinoma has an uncommon eosinophilic variant has been recognized for more than a decade. In sections stained with hematoxylin and eosin, the eosinophilic variant of chromophobe renal cell carcinoma and renal oncocytoma are similar in appearance. While it is well established that chromophobe renal cell carcinoma and renal oncocytoma have different patterns of genetic anomalies, little is known of the genetics of the eosinophilic variant of chromophobe renal cell carcinoma. This study was undertaken to elucidate the genetic lesions of eosinophilic chromophobe renal cell carcinoma and to compare them with those found in classic chromophobe renal cell carcinoma and in renal oncocytoma. A total of 29 renal neoplasms--nine eosinophilic chromophobe renal cell carcinomas, 10 classic chromophobe renal cell carcinomas, and 10 oncocytomas--were investigated by fluorescence in situ hybridization on 5 microm paraffin-embedded tissue sections with centromeric probes for chromosomes 1, 2, 6, 10, and 17. Signals were counted in 100-200 neoplastic nuclei from each tumor. Chromophobe renal cell carcinomas frequently showed loss of chromosomes 1 (70% of classic, 67% of eosinophilic), 2 (90% classic, 56% eosinophilic), 6 (80% classic, 56% eosinophilic), 10 (60% classic, 44% eosinophilic), and 17 (90% classic, 78% eosinophilic); Among the classic chromophobe renal cell carcinomas, only one had no loss of any of the chromosomes, while 50% had loss of all five chromosomes. Among the eosinophilic chromophobe renal cell carcinomas, one of nine had no loss and 44% had loss of all five chromosomes. One oncocytoma had loss of chromosome 1. No other chromosomal loss was detected in the oncocytomas. In conclusion, losses of chromosomes 1, 2, 6, 10, and 17 are frequent in both eosinophilic and classic chromophobe renal cell carcinomas. Loss of chromosome 1 occurs occasionally in oncocytoma but losses of chromosomes 2, 6, 10, and 17 are not found in oncocytomas. When the differential diagnostic problem is oncocytoma vs eosinophilic chromophobe renal cell carcinoma, detection of losses of chromosomes 2, 6, 10, or 17 effectively excludes the diagnosis of oncocytoma and supports the diagnosis of chromophobe renal cell carcinoma.