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

SIMPLE SUMMARY: Five years of therapy remains the standard for adjuvant endocrine therapy in early breast cancer. However, the recurrence risk remains elevated beyond this time period. Estimating the risk of recurrence as well as the efficacy of therapy is important in the selection of patients who will benefit from the extension of adjuvant endocrine therapy. The aim of this review is to summarize the major studies investigating the optimal duration of adjuvant endocrine therapy as well as to elaborate the possible individual indications for the extension of this therapy. ABSTRACT: 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.