Anti-estrogens in the treatment of breast cancer: current status and future directions.

For many years, the non-steroidal estrogen receptor (ER) blocker tamoxifen has been the drug of choice for the treatment of hormone-responsive breast cancer. However, deleterious effects on other tissues such as the endometrium and the frequent occurrence of relapse due to tamoxifen resistance have led to the search for alternative drugs that exhibit more favorable tissue-specific ER effects. Alongside these selective ER modulators, a new generation of aromatase inhibitors, which act by limiting the supply of local estrogen to the breast tumor, has emerged to challenge tamoxifen for supremacy. Together with other novel therapies under investigation, it can be hoped that such drugs may, alone or in combination, lead to better breast cancer treatment.