Extended Adjuvant Endocrine Therapy in Early Breast Cancer Patients—Review and Perspectives

Seventy percent of all breast cancer subtypes are hormone receptor-positive. Adjuvant endocrine therapy in these patients plays a key role. Despite the traditional duration of a 5-year intake, the risk of relapse remains elevated in a substantial proportion of patients. Several trials report that the risk of late recurrence is reduced by the extension of adjuvant endocrine therapy beyond 5 years. However, the optimal duration of endocrine therapy is still a matter of debate. The newer data only show a marginal benefit resulting from extension beyond 7 to 10 years. Furthermore, extension may be associated with more side effects. Thus, the adequate selection of patients qualifying for an extended adjuvant therapy is of importance. Tools/genomic tests, which include the characteristics of the patient and the tumor, may help to better identify patients with a risk of a late relapse. Taken together, the magnitude of benefit for extended adjuvant endocrine therapy is based on the precise estimation of the risk of relapse after 5 years. This must be balanced against the long-term side effects of endocrine treatment and the competing risks. For patients with an intermediate risk, 7 years appears to be the optimal duration, and in those with high-risk features, endocrine therapy up to 10 years may be considered.