Controversies in Adjuvant Endocrine Therapy for Breast Cancer

Overview: Adjuvant endocrine therapy for early-stage breast cancer has had the single biggest impact on improving survival from the disease—with tamoxifen alone contributing to saving many thousands of lives. In postmenopausal women, additional progress has been made by the incorporation of aromatase inhibitors into the treatment of early-stage, estrogen receptor (ER)–positive breast cancer, as several large well-conducted trials have established either “up-front” or “switch” strategies that are now widely used. To date, both have been shown to be beneficial when compared with tamoxifen alone, although controversy exists as to which approach is superior. Increasingly, extended adjuvant therapy is being considered, as “longer may be better” for some women who have an ongoing risk of recurrence beyond 5 years. However, controversy remains as to how long adjuvant endocrine therapy should be given for; in clinical practice, clinicians balance the level of risk for individual patients versus any ongoing toxicity concerns. For premenopausal women, with ER-positive breast cancer, tamoxifen remains the gold standard with uncertainty in the added overall benefit of ovarian suppression. Important clinical trials have recently been completed that may help answers this question, including whether complete estrogen deprivation using a luteinizing hormone releasing hormone (LHRH) agonist plus aromatase inhibitors (AIs) is of added benefit. In recent years, molecular profiling of ER-positive breast cancer has started to distinguish those women with a low risk of recurrence on endocrine therapy who may not need chemotherapy. Thus, with more therapy options and greater tumour stratification, modern, adjuvant endocrine therapy is becoming increasingly personalised to suit each individual patient's risk.