Adjuvant endocrine therapy for breast cancer: how long is long enough?

Although women with early-stage hormone receptor-positive breast cancer have low recurrence rates initially, they have a constant and unrelenting risk of relapse that extends up to 15 years despite the use of adjuvant therapy. Increasing evidence supports the use of extended endocrine therapy with either tamoxifen or an aromatase inhibitor (AI) after 5 years of initial adjuvant tamoxifen to reduce breast cancer recurrence and mortality. However, the optimal total duration of AI therapy, as well as the ideal timing of sequencing from tamoxifen to an AI, is still unclear. Potential strategies differ depending on a woman's menopausal status at the time of her initial diagnosis. Individual patient clinical factors and preferences can help with decision making until further data emerge on prolonged AI use and on potential biomarkers that can be used to tailor adjuvant endocrine treatment.