These types of medications work well for women with breast cancer tumours that are dependent on estrogen and progesterone in order to survive and spread.
Tamoxifen is known as a selective estrogen receptor modulator (SERM). Tamoxifen binds to cells, blocking estrogen from attaching to them and preventing the estrogen from feeding the tumour. Tamoxifen has been shown to help prevent breast cancer in women who are at high risk of developing breast cancer, to help destroy cancer cells, and also to help prevent the cancer from coming back.
Tamoxifen is taken as a pill by mouth and is usually given once a day for up to 5 years. There has not been any additional benefit shown from taking it for a longer period of time.
Common side effects associated with tamoxifen are menopausal-like symptoms, such as hot flashes, night sweats, and vaginal dryness. Side effects that are more serious but less common include blood clots in the legs or lungs and endometrial cancer (cancer of the uterus). Tamoxifen also has a protective effect on your bones and can be helpful for women who have osteoporosis or are at risk for developing osteoporosis. For these reasons, it is important to discuss with your doctor whether this medication is best for you.
Aromatase inhibitors, such as anastrozole (Arimidex®), letrozole (Femara®), and exemestane (Aromasin®), work by blocking the production of estrogen by the tissues in postmenopausal women. These medications do not block the production of estrogen by the ovaries, so they do not work in premenopausal women unless surgery is done or medications are given to stop the ovarian production of estrogen.
Aromatase inhibitors have typically been used to treat women with breast cancer that has returned; however, there has been a lot of research in the past decade to suggest that these medications also work well in women who have recently been diagnosed with breast cancer, either to help kill the cancer cells or to help prevent the cancer from coming back, even after tamoxifen has been used. In some situations, the aromatase inhibitors have been compared with tamoxifen and have been shown to do just as well or even better. All 3 of the commonly used aromatase inhibitors are available in a tablet that is given once a day for a period of up to 5 years.
The main side effects associated with aromatase inhibitors include hot flashes and muscle or joint pain. There is no increased risk of blood clots or endometrial cancer with these medications; however, there may be an increased risk of osteoporosis and fractures. There is little information currently regarding the long-term side effects of aromatase inhibitors, so careful discussion with your doctor is recommended.
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