Breast cancer that is very aggressive, recurring within a year of the initial breast surgery or involving the liver, is usually treated with intravenous chemotherapy rather than tamoxifen. On the other hand, breast cancer that occurs more than two years from surgery, involves only the bone or soft tissues, and tests positive for estrogen receptors is treated with tamoxifen. This latter, less aggressive form of breast cancer is much more common in clinical practice. When tamoxifen is used in this latter setting, about half of women benefit from treatment with either a shrinkage or stabilization of the tumor. This benefit on average lasts about a year, although some women are free of recurrent tumor for more than five years.
Some women respond to tamoxifen better than others.
Cancers that do not have the estrogen receptor do not seem to respond to tamoxifen. Premenopausal women respond to tamoxifen, but postmenopausal women seem to respond better. In premenopausal women, an agent may be added to tamoxifen for added response. This agent is injected under the skin every three months and indirectly tells the ovaries to stop making estrogen.