Comparison of MIB-1 proliferation rates for eosinophilic renal tumors - Oncocytoma, chromophobe renal carcinoma, and eosinophilic variant of renal carcinoma

Eosinophilic renal tumors comprise a group of tumors that may have overlapp ing morphologic features, including oncocytoma (O), chromophobe renal cell carcinoma (CCC), and granular or eosinophilic cell carcinoma (ECC). The ove rlap of cytologic atypia is well described, but there are no data on the pr oliferation indices (PI) of these tumors. This study investigates the PI of these tumors to ascertain correlations of morphologic parameters and wheth er PI is diagnostically useful in separating them. We contributed a total o f 21 oncocytomas, 32 CCC, and 12 ECC for this study. Histologic sections we re examined, and immunoperoxidase was performed by the ABC technique with a ntigen retrieval. MIB-1 index was generated manually by counting the number of positive nuclei in 25 high-power fields. The PI for each group was comp ared with tumor size, cytologic atypia, and the PI among all three groups w as compared. There was substantial overlap of the PI between O and CCC, wit h no significant difference of index means, yet 76% of O and only 28% of CC C had an index >0.24. The mean index of tumors with index >0.24 was signifi cantly higher for CCC compared with O. There was no correlation between the PI, tumor size, or morphology between O and CCC. The PI of ECC was markedl y higher than the PIs of O and CCC. Our conclusions are as follows: (1) PI for O and CCC are markedly lower than for ECC; (2) PI cannot be used to dis tinguish between O and CCC; and (3) There is a subset of CCC with markedly elevated PI. Only meaningful clinical follow-up will substantiate the use o f PI as a prognostic factor for CCC.