Endocrine Treatment of Breast Cancer: Current Perspectives, Future Directions

Breast cancer remains one of the major causes of death in women, and endocrine treatment is currently one of the mainstay of treatment in patients with estrogen receptor positive breast cancer. Endocrine therapy either slows down or stops the growth of hormone-sensitive tumors by blocking the body’s capability to yield hormones or by interfering with hormone action. In this paper, we intended to review various approaches of endocrine treatments for breast cancer highlighting successes and limitations. There are three settings where endocrine treatment of breast cancer can be used: neoadjuvant, adjuvant, or metastatic. Several strategies have also been developed to treat hormone-sensitive breast cancer which include ovarian ablation, blocking estrogen production, and stopping estrogen effects. Selective estrogen-receptor modulators (SERMs) (e.g. tamoxifen and raloxifene), aromatase inhibitors (AIs) (e.g. anastrozole, letrozole and exemestane), gonadotropin-releasing hormone agonists (GnRH) (e.g. goserelin), and selective estrogen receptor downregulators (SERDs) (e.g. fulvestrant) are currently used drugs to treat breast cancer. Tamoxifen is probably the first targeted therapy widely used in breast cancer treatment which is considered to be very effective as first line endocrine treatment in previously untreated patients and also can be used after other endocrine therapy and chemotherapy. AIs inhibit the action of enzyme aromatase which ultimately decrease the production of estrogen to stimulate the growth of ER+ breast cancer cells. GnRH agonists suppress ovarian function, inducing artificial menopause in premenopausal women. Endocrine treatments are cheap, well-tolerated and have a fixed single daily dose for all ages, heights and weights of patients. Endocrine treatments are not nearly as toxic as chemotherapy and frequent hospitalization can be avoided. New drugs in preliminary trials demonstrated the potential for improvement of the efficacy of endocrine therapy including overcoming resistance. However, the overall goals for breast cancer including endocrine therapy should focus on effective control of cancer, design personalized medical therapeutic approach, increase survival time and quality of life, and improve supportive and palliative care for end-stage disease.