Tumor growth is not inhibited by fulvestrant. A. Western blot showing that treatment of 4G-shp53-PI3K tumor cells with 1 μM fulvestrant reduces the level of ERα. B&C. Fulvestrant has no effect on proliferation of the cells measured by crystal violet staining (B) or growth curves (C; fulvestrant treatment was started at the arrow; n = 3; NS, not significant). D. 4G-shp53-PI3K cells were injected into the ducts, allowed to form tumors for 3 weeks then treated with fulvestrant or vehicle for 5 weeks. Representative immunohistochemical images show a marked reduction in ERα level in treated tumors. Each image is derived from a separate animal (n = 6 for control, n = 7 for fulvestrant). The slides were all processed together. Scale bars in F, 50 μm. E&F. 4G-shp53-PI3K cells were injected into the ducts, allowed to form tumors for 3 weeks then treated with fulvestrant or vehicle for 3 weeks. E. PhotonIMAGER scans of excised mammary glands after treatment with fulvestrant or vehicle (control) to show how the response was quantified. The scanner counts fluorescence emitted by tdTomato. F. Quantitative data from the glands in E (n = 8 for control, n = 9 for fulvestrant; NS, not significant).