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No kind of cancer is more common in women than breast cancer. Every year, worldwide, over 2.7 million women are diagnosed with breast cancer, and over 500,000 women die of it. In Western countries, one in eight women will eventually be diagnosed with the disease, although the risk is lower for women in other parts of the world.
Until the 1990’s, there was very little women could do to prevent breast cancer other than to pursue a healthy lifestyle and hope for the best. With the advent of selective hormone receptor modulators, however, breast cancer prevention has become possible, although it’s not a perfect process.
What Is a Selective Hormone Receptor Modulator?
Many, although not all, breast cancers are fueled by hormones. When breast cancer tumors are removed, they are biopsied to determine whether the cancer is:
- Endocrine receptor positive, that is, having receptor sites for either estrogen or progesterone, or both, which stimulate the growth of tumors,
- HER2 positive, having receptor sites for a growth factor that also stimulates growth of tumors,
- Triple-receptor positive, having receptor sites for estrogen, progesterone, and HER2, or
- Triple-receptor negative, having no receptor sites for any of the three tumor growth factors.
In some women estrogen, progesterone, and/or HER2 stimulate the growth of cancer. Blocking the action of estrogen, progesterone, and/or HER2, in those women, blocks the growth of cancer. Receptor blockers won’t have any effect in women who don’t have the receptors, but in some women, they could make a huge difference in the risk of recurrence of cancer. To that end, pharmaceutical companies have developed:
- Tamoxifen, also known as TMX and marketed under the trade name Nolvadex, to block estrogen receptors. Another drug called fulvestrant (marketed as Faslodex) at first blocks the estrogen receptor and then destroys it.
- Megestrol acetate (Megace) to block progesterone receptors.
- A monoclonal antibody trastuzumab (marketed as Herceptin) to block HER2 receptors.
All of these treatments have been around for about 25 years. They are well known, and their cost has been greatly reduced. Many health insurance programs, even in the United States, cover them for women who have had breast cancer treatment.
How Well Do Drugs for Breast Cancer Prevention Work?
These drugs are typically given to prevent a recurrence of breast cancer, rather than the first appearance of the disease. In women who have been treated for breast cancer in the past:
- About 60 percent of women whose tumors were estrogen- or progesterone-receptor positive have a partial or complete response to tamoxifen. (It won’t help women who are triple-receptor negative.)
- Megace helps up to 90 percent of women who have had breast cancer maintain appetite and avoid wasting. This indirectly extends life.
- Herceptin prolongs life in about 93 percent of women who use it, and it prevents return of the cancer in about 74 percent, although it can cause severe heart damage if it is used for longer than one year.