From the FDA Drug Label
The growth of some cancers of the breast is stimulated or maintained by estrogins. Treatment of breast cancer thought to be hormonally responsive (i.e., estrogen and/or progesterone receptor positive or receptor unknown) has included a variety of efforts to decrease estrogen levels (ovariectomy, adrenalectomy, hypophysectomy) or inhibit estrogen effects (antiestrogins and progestational agents). In postmenopausal women, estrogins are mainly derived from the action of the aromatase enzyme, which converts adrenal androgens (primarily androstenedione and testosterone) to estrone and estradiol. The suppression of estrogen biosynthesis in peripheral tissues and in the cancer tissue itself can therefore be achieved by specifically inhibiting the aromatase enzyme.
The role of endocrine therapy in the treatment of breast cancer is to decrease estrogen levels or inhibit estrogen effects in hormonally responsive breast cancer. This can be achieved through various methods, including:
- Aromatase inhibition: using drugs such as exemestane or letrozole to inhibit the aromatase enzyme, which converts androgens to estrogins.
- Antiestrogins: using drugs such as tamoxifen to block the effects of estrogen on breast cancer cells.
- Ovariectomy, adrenalectomy, or hypophysectomy: surgical removal of the ovarins, adrenal glands, or pituitary gland to decrease estrogen production.
- Progestational agents: using progesterone-like drugs to inhibit estrogen effects. Endocrine therapy is used in the adjuvant treatment of postmenopausal women with estrogen-receptor positive early breast cancer, as well as in the treatment of advanced breast cancer in postmenopausal women whose disease has progressed following tamoxifen therapy 1 2.