Extending Adjuvant Endocrine Therapy in Breast Cancer: Who, What, Why?

Adjuvant endocrine therapy provides substantial benefit by reducing breast cancer recurrences and improving associated mortality in early-stage endocrine-responsive breast cancers (estrogen receptor- and/or progesterone receptor-positive). Residual risk of relapse, even after completion of 5 years of adjuvant endocrine therapy, has fueled development of extended therapy (beyond 5 years) trials. However, several questions remain when recommending extended adjuvant endocrine therapy, such as those concerning patient selection, agent of choice, use of biomarkers or clinical variables to assess residual risk of relapse, and duration of treatment. In this article, we will provide a case-based expert opinion on: 1) the duration of extended adjuvant endocrine therapy in both premenopausal and postmenopausal women; 2) use of biomarkers in guiding this decision; and 3) toxicities to be considered when recommending extended adjuvant endocrine therapy. We also provide key factors to consider, including patient preference, when guiding our patients in this important treatment decision.