Tamoxifen (brand name Nolvadex) has been effectively used in treating breast cancer for over 25 years.  The drug works by stemming the hormone estrogen, which in turn prevents the growth or spread of new cancer cells.  Tamoxifen was long thought to be most effective if taken for just five years immediately following surgery for breast cancer.  Recent studies have shown that other drugs that are called aromatase inhibitors. 

When tamoxifen is taken after surgery it can reduce the chance of a breast cancer recurrence by as much as 50%.  Usually these positive effects occur if the breast cancer is detected and diagnosed early and if the cancer had estrogen or progesterone receptors.  Tamoxifen can also be effective in treating metastatic breast cancer and be used in stopping cancer development in women that have a high risk.

Tamoxifen works by blocking estrogen receptors and thereby stopping estrogen from causing cancer growth.  Breast cancer is typically very sensitive to estrogen and can grow quite quickly and largely with estrogen.  Estrogen, a naturally occurring hormone in women, binds to estrogen receptors in cancer cells.  This binding causes the cancer cells to grow quicker and larger than they would without the estrogen. 

Many breast cancers are known as estrogen receptor positive cancers because of their susceptibility to estrogen related growths.  When Tamoxifen is added to the body it works by shutting down this growth.  This action is especially effective following breast cancer removal or treatment.  Tamoxifen can also help in preventing breast cancer from metastasizing, or spreading to other parts of the body, including the other breast.

Side effects of tamoxifen include the rare development of uterine cancer, which, when monitored for, is effectively treated and cured with surgery.  Signs of developing uterine cancer related to tamoxifen include vaginal bleeding.  Blot clots may form from taking tamoxifen as well.  Other less severe and more common side effects include hot flashes, vaginal discharge, and mood swings.
 
Most patients taking tamoxifen report a marked reduction in breast cancer risk and the side effects seem minor in comparison with what the drug is preventing.  Newer studies and drugs on the market have shown an even greater rate of breast cancer prevention. 

As recent as October of 2005, the drug Herceptin has shown a good success rate in treating early stage breast cancer.  For a long time, Herceptin was only used as a latter stage measure in advanced breast cancer patients.  Recent studies have shown that the drug is effective in attacking early cancer cells as well as more advanced ones.

Tamoxifen needs to be administered for at least two or three years after surgery in order for the medicine to be effective.  Other recent studies have shown that when a few years of tamoxifen therapy is followed by other medication it can have a more effective cure rate than tamoxifen alone.