Hormone Therapy for Breast Cancer

About two-thirds of women with breast cancer have tumors that contain estrogen receptors (called ER-positive). This type of cancer depends on the female hormone to grow. Hormone therapy is given to block the body's naturally occurring estrogen and fight the cancer's growth. Women who are ER-positive are more likely to respond to hormone treatment than women who are ER-negative.

Tamoxifen for Breast Cancer

Tamoxifen is a pill taken daily and has been used consistently for the past decade to treat breast cancer. Tamoxifen can be used in women of any age, regardless of whether they've gone through menopause. Long-term (five-year) use of this anti-estrogen drug has been found to reduce the chance of breast cancer recurrence and new breast cancers in women with ER-positive or ER-unknown breast tumors. Doctors also use tamoxifen to treat metastatic breast cancer. There is no advantage in taking tamoxifen for more than five years.

Women taking tamoxifen are more likely to develop cancer of the uterus (endometrial cancer) than other women. Therefore, they should have regular pelvic exams and tell their doctor about any abnormal uterine bleeding. Other risks include deep-vein thrombosis, blood clots in the lungs, and benign ovarian cysts. Minor side effects include hot flashes, mood swings, and cataracts.

Aromatase Blockers and Breast Cancer

Aromatase blockers are pills that appear to be more effective in treating breast cancer than tamoxifen, according to new studies. But they are effective only in women who are past menopause. Aromatase blockers - used in both early and advanced breast cancer - prevent estrogen from being produced in the first place. They inhibit or inactivate the aromatase enzyme, which is involved in the production of estrogen.

Arimidex (anastrozole) and Femara (letrozole) are aromatase blockers used to treat estrogen receptor positive breast cancer in postmenopausal women, either following tamoxifen treatment or as first line therapy. A 2008 study showed that women taking Femara reduced their risk of their cancer returning by 63%. That's several years after completing the recommended five years on tamoxifen.

Positive results have also been demonstrated with Arimidex. One study found that switching to Arimidex after 2 to 3 years of tamoxifen was linked to better survival without disease recurrence at the 5-year mark compared with staying on tamoxifen for 5 years.

A third pill, Aromasin (exemestane), is used for women with early breast cancer after 2 to 3 years of tamoxifen treatment. In clinical research, compared to women that continued tamoxifen for 5 years, women who switched to Aromasin after 2 to 3 years of tamoxifen had a 31% lower risk of breast cancer recurrence and a 14% decrease in mortality.

Aromasin is also used for women with advanced breast cancer when tamoxifen stops working. It is only used in women after menopause.