1.   Both drugs can block estrogen, which often promotes breast cancer growth.

2.   Danazol shrinks fibroids by blocking estrogen, but it shrinks breasts and causes growth of facial hair and acne.

3.   Tamoxifen and raloxifene are successful because they can block estrogen from reaching the breast, Arnot said.

4.   Tamoxifen, on the other hand, blocks estrogen from binding to receptors in breast cells.

5.   Tamoxifen works by blocking estrogen from reaching cancer cells.

6.   The aromatase inhibitors also block estrogen, although in a different way.