Breast cancer is the most common type of cancer in women. The National Cancer Institute estimates that nearly 193,000 women will be diagnosed with breast cancer in 2009.
1 For women in the U.S., breast cancer is the third leading cause of cancer deaths.
Women who are diagnosed with early-stage breast cancer usually require three or four types of treatment: 1) surgery to remove the cancer (either lumpectomy or mastectomy); 2) radiation to reduce the size of the tumor or reduce the chances of it coming back (usually used for lumpectomy patients but not mastectomy patients); 3) chemotherapy to reduce the size of the tumor or reduce the chances of it coming back (for lumpectomy or mastectomy patients); 4) and hormone treatment to reduce the chances of the cancer coming back. In addition to its use for women who are diagnosed with breast cancer, hormone treatment is sometimes used to try to prevent breast cancer for women at high risk, such as those with mothers or sisters who were diagnosed with breast cancer. However, there are risks as well as benefits to hormone treatment, and tamoxifen, the most common and most studied type of hormonal treatment, is no longer considered the most effective treatment for post-menopausal women.
What is Hormone Treatment?
Hormonal treatment for breast cancer is very different from hormone therapy for menopause. The other name for hormonal therapy for cancer is "anti-estrogen therapy." The goal of hormonal treatment (or anti-estrogen therapy) is to starve the breast cancer cells of the hormone they thrive on, which is estrogen. Hormone treatment is effective for women with estrogen receptor-positive breast cancer (the most common type of breast cancer) and ductal carcinoma in situ (DCIS), which is also known as non-invasive or stage zero breast cancer. Hormone treatment is not effective for women with
estrogen-receptor negative breast cancer.
For women who have already gone through menopause before being diagnosed with breast cancer, aromatase inhibitors seem to be more effective than tamoxifen. Aromatase is the enzyme that produces estrogen in postmenopausal women. Interfering with the production of estrogen triggered by aromaterse reduces the amount of estrogen in the body, helping to starve breast cancer cells by depriving them of estrogen.
The Use of Hormone Treatment for Postmenopausal Women
Short-term research on postmenopausal women has indicated that aromatase inhibitors alone, or after 2-5 years of tamoxifen, results in a significant but modest increase in cancer-free survival compared with tamoxifen alone. However, there is no difference between tamoxifen and aromatase inhibitors for
overall survival for postmenopausal women. Moreover, there is no long-term data on aromatase inhibitors. And, since aromatase inhibitors do not block the production of estrogen from the ovaries, they are not usually used in premenopausal women. Studies are under way, but there are no available data on aromatase inhibitors for premenopausal women or for treatment of DCIS.
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Tamoxifen improves survival rates from 65% to 74% over 15 years and reduces recurrence from 45% to 33% over 15 years in premenopausal and postmenopausal women with estrogen receptor-positive tumors.
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The combination of tamoxifen and chemotherapy benefits premenopausal and postmenopausal women with hormone receptor-positive breast cancer. For example, in postmenopausal women, 3-year disease-free survival was increased from 67% to 84% by a combination of chemotherapy (doxorubicin and cyclophosphamide) plus tamoxifen;
1 The optimal length of tamoxifen therapy, appears to be 5 years.
3 One to two years is less effective. Tamoxifen therapy should not be continued for
more than 5 years.
3 In women with DCIS who undergo lumpectomy or other types of breast conservation, tamoxifen reduces breast cancer events and the incidence of cancer in the other breast.
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Aromatase inhibitors are approved as a first-line treatment of
d women with estrogen receptor-positive breast cancer of all stages. The three current aromatase inhibitor treatment options are 5 years of aromatase inhibitor therapy, two to three years of tamoxifen followed by two to three years of aromatase inhibitor therapy, or 5 years of tamoxifen followed by 5 years of aromatase inhibitor therapy for postmenopausal women. When tamoxifen alone was compared with an aromatase inhibitor (exemestane, letrozole, or anastrozole), and with tamoxifen followed by each aromatase inhibitor, cancer-free survival was higher for the aromatase inhibitor or for two to three years of tamoxifen followed by an aromatase inhibitor.
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Side effects of tamoxifen and aromatase inhibitors
Tamoxifen increases the chances of a woman developing endometrial cancer and blood clots in the vein, especially for women over 50 years of age.
1,4 Tamoxifen therapy also often causes side effects that are similar to those experienced in menopause, including hot flashes and irregular periods.
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Aromatase inhibitors increase the risk for osteoporosis compared with tamoxifen or placebo. Exemestane, a commonly used aromatase inhibitor, also increases the risk for visual disturbances, joint pain, an allergic reaction to medication, or diarrhea. Letrozole, another aromatase inhibitor, also called Femara) increases the risk for cardiac events.
These side effects can be fatal or can harm a patient's quality of life. Close monitoring of women for symptoms, such as abnormal uterine bleeding, is needed, and women taking tamoxifen should receive annual pelvic exams.
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