Endocrine therapy of breast cancer

Breast cancer remains one of the first leading causes of death in women, and currently endocrine treatment is of major therapeutic value in patients with estrogen-receptor positive tumors. Selective estrogen-receptor modulators (SERMs), such as tamoxifen and raloxifene, aromatase inhibitors, and GnRH agonists are the drugs of choice. Tamoxifen, a partial nonsteroidal estrogen agonist, is a type II competitive inhibitor of estradiol at its receptor, and the prototype of SERMs. Aromatase inhibitors significantly lower serum estradiol concentration in postmenopausal patients, having no detectable effects on adrenocortical steroids formation, while GnRH agonists suppress ovarian function, inducing a menopause-like condition in premenopausal women. Endocrine therapy has generally a relatively low morbidity, leading to a significant reduction of mortality for breast cancer. The aim of chemoprevention is to interfere early with the process of carcinogenesis, reducing the risk of cancer development. As preventive agents, raloxifene and tamoxifene are equivalent, while raloxifene has more potent antiresorptive effects in postmenopausal osteoporosis. Endocrine treatment is usually considered a standard choice for patients with estrogen-receptor positive cancers and non-life-threatening advanced disease, or for older patients unfit for aggressive chemotherapy regimens. Several therapeutic protocols used in patients with breast cancer are associated with bone loss, which may lead to an increased risk of fracture. Bisphosphonates are the drugs of choice to treat such a drug-induced bone disease. The aim of this review is to outline current understanding on endocrine therapy of breast cancer.