Brenda Spriggs, MD, MPH, MBA
Many cases of breast cancer are estrogen-responsive, which means the tumor grows in response to estrogen. Tamoxifen is a therapeutic agent designed to block the effects of estrogen. It can be used to prevent the development of cancer in high-risk patients, such as those with a family history of breast cancer, or to treat existing breast cancer. Tamoxifen, however, can lead to a number of side effects, and cancers treated with Tamoxifen can eventually become resistant to the drug. A number of alternative treatments are available to patients who respond poorly to Tamoxifen.
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Raloxifene, trade name Evista, is an estrogen-blocking drug that can serve as an alternative to Tamoxifen. It belongs to a class of estrogen inhibitors called selective estrogen response modulators. Evista works by blocking the activation of estrogen receptors on breast cells to prevent estrogen signaling. Prescribing Evista to patients with a high risk of developing breast cancer may prevent cancer development by disrupting estrogen signaling in the breast.
Evista is only prescribed to post-menopausal women, according to Lilly, the drug's manufacturer. It is prescribed for the treatment of breast cancer or as a treatment for osteoporosis with the additional function of protecting against breast cancer development. Women taking Evista are at an increased risk of developing blood clots.
Anastrozole, trade name Arimidex, is another alternative to Tamoxifen therapy. Arimidex belongs to a class of drugs called aromatase inhibitors, which work to prevent estrogen production. The molecular structure of estrogen is based on existing cholesterol-like chemicals in cells and specific proteins are responsible for generating estrogen. Anastrozole works by inhibiting key proteins involved in estrogen synthesis, stopping the production of estrogen and lowering estrogen levels.
Arimidex is approved to treat initial cases of metastatic breast cancer in post-menopausal women, and can also be taken to prevent breast cancer recurrence. AstraZeneca Pharmaceuticals, Arimidex's manufacturer, reports that taking Arimidex may worsen existing cardiovascular conditions, as well as cause bone weakness, nausea or allergic reactions.
Medroxyprogesterone, trade name Provera, is another hormone-based cancer therapy that may serve as an alternative to Tamoxifen. Provera is a synthetic chemical that acts similarly to progesterone, another hormone responsible for signaling in breast cells. The exact mechanism by which Provera works to fight cancer is not yet known, but it may disrupt estrogen signaling or directly kill cancer cells, according to MacMillan Cancer Support.
Provera is prescribed for breast cancer cases that have become resistant to Tamoxifen or other hormone therapy. MacMillan reports that Provera can lead to increased appetite, fluid retention, irregular vaginal bleeding and mood changes.