The immunohistochemical staining of Fra-1 in benign breast tumors. Paraffin-embedded tissue sections were prepared. Endogenous peroxidase activity was quenched using 3% hydrogen peroxide before immunohistochemical staining. The Streptavidin-Biotin method was used to detect Fra-1 expression. The rabbit anti-human Fra-1 polyclonal antibody at a concentration of 5 μg/ml in PBS was applied for 60 minutes at 37°C or overnight at 4°C. The sections were then incubated with biotinylated anti-rabbit antibody at 37°C for 15 minutes. The streptavidin peroxidase reagent was applied at 37°C for 15 minutes. The color was developed by incubating with DAB solution. A, nonspecific immunoglobulin was used as a negative control. B, The nuclear immunoreactivity for Fra-1 was identified mostly in the epithelial cells of fibroadenomas. C, The strong nuclear immunostaining was present in fibroadenomas. D, Positive staining appeared largely on the apical epithelial layer on the luminal aspect, but myoepithelial layer was mostly negative. ×400 magnification.