For immunohistochemistry on formalin-fixed, paraffin-embedded specimens adequate pretreatment of the sections to achieve an unmasking of antigenic domains before staining the specimens is necessary. In this study, we compared the effect of microwave and autoclave heating on the expression of the cell proliferation marker Ki-67 (Mib-1) in renal cell carcinomas. A total of 177 formalin-fixed and paraffin-embedded tumor specimens of locally confined renal cell carcinomas with clear cell morphology were investigated. Two different antigen unmasking techniques were used: microwave and autoclave heating. The fraction of Ki-67 positively stained nuclei was determined in APAAP (alkaline phosphatase-antialkaline phosphatase) stained slides. The fraction of Mib-1-labelled cells was significantly higher after autoclave compared to microwave pretreatment (mean value 4.95 vs. 1.43, p<0.001). We recommend the autoclave heating technique for quantitative detection of Ki-67 with the Mib-1 antibody in renal cell carcinomas.

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