Renal cell carcinoma with mixed features of papillary and clear cell cytomorphology: a fluorescent in situ hybridization study.

We performed fluorescent in situ hybridization (FISH) to investigate the numeric change of chromosomes 7, 17, and Y and loss of chromosome 3p in "papillary renal cell carcinomas (RCC) with extensive clear cell changes (CCC)." Consecutive cases of RCC over a 12-year period were reviewed to identify "papillary RCC with extensive CCC." Immunostaining for cytokeratin 7 and alpha-methylacyl-CoA racemase (AMACR) and FISH for chromosomes 7, 17, Y, and 3p were applied. Of the total of 521 RCC retrieved, there were 49 RCC with papillary architecture and clear cell areas that could be divided into: Group 1 (12 cases), typical clear cell RCC with focal areas of papillary formation; Group 2 (28 cases), focal typical papillary RCC having papillary architecture with extensive CCC; and Group 3 (nine cases), RCC with an admixture of eosinophilic/clear cytoplasm and solid/papillary architecture. Group 1 showed negative immunoreactivity for CK7 and AMACR and absence of numeric chromosomal gain or loss of chromosomes 7/17 and Y. Groups 2 and 3 showed variable reactivity for CK7 and AMACR. Tumors in group 2 and five in group 3 showed trisomies of chromosomes 7 and/or 17 with or without loss of chromosome Y. Loss of small arm 3p was observed in groups 1 and 3 but not in group 2 tumors. In conclusion, papillary RCC may show phenotypical CCC mimicking clear cell RCC. In a small number of cases with mixed histopathological features, FISH is helpful in subtyping RCC.