This year in the United States of America, 212,000 women will be diagnosed with breast cancer and 30,000 or more will die from it. Other than skin cancer, breast cancer is the second most commonly diagnosed cancer in women. Hormones such as estrogen play an important role in breast cancer and regulating the action of estrogen can play an important role in reducing breast cancer recurrence.
Estrogen and Breast Cancer
The hormone estrogen impacts on the biology of many tissues and organs but its major targets are the breast and uterus, where it plays a critical role in cell proliferation. Cells that line the ducts of the milk-producing glands in the breast respond to estrogen by proliferating, a normal event during the menstrual cycle to prepare the breast for milk production should pregnancy occur. At the end of the menstrual cycle estrogen levels decrease and the proliferating cells die off. In the case of breast cancers that are positive for the presence of the estrogen receptor, the presence of the hormone helps the cancer cells to proliferate.
Anti-estrogen Therapy for Breast Cancer
If a breast cancer is responsive to the presence of estrogen then it only makes sense that interfering with the action of estrogen on these cells would help to limit their proliferation. This is where anti-estrogen drugs play an ever-increasing role in the treatment of patients with estrogen receptor-positive breast cancer. Several studies have shown the benefit of anti-estrogen therapies in reducing the recurrence rate of breast cancer. In addition more recent data has shown the usefulness of anti-estrogen therapy in reducing the risk of developing breast cancer in women whose family history puts them at high risk for breast cancer occurrence. The drug tamoxifen (commercial name Nolvadex) has been available and in use since the 1970s. A more recently available anti-estrogen compound known as raloxifene (commercial name Evista) was originally characterized as a treatment for osteoporosis (bone is also a target of estrogen action).
Tamoxifen Versus Raloxifene
The results of the STAR clinical trial funded by the US National Cancer Institute (NCI) showed that raloxifene was as effective as tamoxifen in reducing the risk of occurrence of invasive breast cancer in post-menopausal women. In addition, raloxifene showed a lower occurrence of certain side effects associated with anti-estrogen therapy using tamoxifen. Tamoxifen therapy can cause an increase in the occurrence of blood clots, uterine cancer and cataracts. Raloxifene therapy was associated with a lower incidence of uterine cancer. However, tamoxifen also appears to be effective in preventing the occurrence of non-invasive breast cancers while raloxifene is not.
Anti-estrogen therapies are a mainstay of current treatment for breast cancer and as chemopreventive agents in populations at high risk for the occurrence of breast cancer. Ongoing clinical trials will likely provide data that only add to their usefulness.
As always, speak with your physician about any medical decision and treatment.
