What is the role of tamoxifen in the treatment of breast cancer?

Chemotherapy: Tamoxifen is a very effective drug for the treatment of hormone-sensitive (estrogen receptor +) breast cancers. It may be used alone or in combination with traditional IV chemotherapy, depending on the cancer stage. Furthermore, tamoxifen has been shown to be effective reducing the chance of developing breast cancer in high-risk women ("chemoprevention").

Anti-estrogen: Tamoxifen is one of the anti-estrogen agents used to treat breast cancer. Cancers that exhibit an estrogen receptor (er positive tumors) are treated in part by blocking the estrogen that act as signals to these tumors to grow.