Raloxifene and Tamoxifene: Drugs for Breast Cancer Prevention

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Estrogen is a female steroid hormone produced mainly in the ovaries. It is important in stimulating the development of secondary sexual characteristics in females during puberty. It has also roles in maintaining cellular metabolism, preparing the breasts for milk production during pregnancy, as well as controlling the growth of uterus linings before women menstruate (Microsoft Encarta 2008).

Relation of Estrogen to Breast Cancer

There are breast cancer cells that are stimulated by estrogen to multiply. These cancer cells have estrogen receptors in their plasma membranes; when estrogen bind to these receptors, cancer cells divide in an abnormal behavior and produce more cancer cells that can metastasize to nearby tissues.

Studies show that women who have longer years of menstruation have higher risk of developing breast cancer than those who reach the menopause stage early. The reason behind this is that the breast tissues are exposed to estrogen for many years since estrogen production is at peak during menstruation (WebMD 3).

Research also shows that women who get pregnant late (say 35 and above) are also at higher risk of developing breast cancer. The hormone estrogen may also be the underlying cause behind this phenomenon (WebMD 3).


The original use of raloxifene, also called Evista (brand name), is to treat osteoporosis in post-menopausal women but researchers noticed that there is a “lower rate of invasive breast cancer” to women who took the drug. Invasive breast cancer is the type of cancer that can metastasize from the breast towards the nearby tissues. Raloxifene is a selective estrogen receptor modulator (SERM) that acts as estrogen in some body tissues (e.g. liver, uterus, bone) but not on others (e.g. breast tissues). The actual biological mechanism on the ability of raloxifene to prevent invasive breast cancer is still unknown but scientists speculate that it prevent the natural estrogen from binding to the estrogen receptor located in the plasma membranes of breast cells. Using this drug, tumors in the breast that need estrogen for growth are not allowed to grow further, preventing the development of a highly fatal invasive cancer. (WebMD 1)

From just an anti-osteoporosis drug, the Food and Drug Administration (FDA) has officially approved raloxifene as the second drug (after tamoxifen) used for the prevention of breast cancer.

The drawbacks of raloxifene are the side effects associated to it like blood clots, strokes, cataract, uterine cancer and others. Women who currently have invasive breast cancer or who have had in the past cannot use it. (WebMD 1)


Tamoxifen is the first FDA approved drug for the prevention of breast cancer in women. It has been in the market for more than 25 years carrying the brand name Nolvadex. It is also a selective estrogen receptor modulator (SERM) that has a mode of action similar to raloxifene described above. (WebMD 2)

The drug, like raloxifene, is used in the prevention of osteoporosis and invasive breast cancer in women. It hinders the increase in number of healthy breast cells which consequently decreases the probability of forming cells with damaged DNA; these cells can undergo abnormal cellular division leading to the formation of tumors or cysts. According to a research funded by the National Cancer Institute (NCI) in the 1990s, high-risk women who took the drug daily for an average of four years are 45% less likely to develop breast cancer than women who took the drug in placebo manner. (WebMD 2)

Unlike raloxifene that is only administered in postmenopausal women, tamoxifene can be used to treat advanced and early stage breast cancer immediately after surgical operation of the breast. It can also help prevent the development of cancer in the second breast after the occurrence of cancer in the first breast.

Tamoxifen has similar side effects to raloxifene and quite expensive. (WebMD 2)


WebMD 1: “Evista for Breast Cancer Prevention” Retrieved from https://www.webmd.com/breast-cancer/evista-for-breast-cancer-prevention?page=1 January 25, 2009.

WebMD 2: “Tamoxifen for Breast Cancer Treatment and Prevention” Retrieved from https://www.webmd.com/breast-cancer/tamoxifen-for-breast-cancer-treatment-and-prevention?page=1 january 25, 2009

WebMD 3: “Breast Cacer Prevention” Retrieved from https://www.webmd.com/cancer/tc/ncicdr0000257994-breast-cancer-prevention%20%20January%2025 January 25, 2009.

“Estrogen.” Microsoft® Student 2008 [DVD]. Redmond, WA: Microsoft Corporation, 2007.