Evaluating the Role of Extended Aromatase Inhibitor Therapy in Early Hormone-Positive Breast Cancer

Purpose of Review: As adjuvant therapy for early-stage, hormone receptor-positive breast cancer has improved, late recurrences have become a significant issue. Endocrine therapies such as tamoxifen and aromatase inhibitors play a central role in reducing the risk of recurrence of hormone-positive breast cancers. However, the continued risk of breast cancer recurrence even with 5 years of adjuvant AI therapy has led to interest in extended therapy. This review intends to discuss and analyze recent trials that have reported results with extending AI therapy beyond 5 years of treatment. Recent Findings: The IDEAL, DATA, and NSABP B-42 were unable to demonstrate a significant benefit in disease-free survival for extending aromatase inhibitor therapy beyond 5 years. They collectively demonstrate a decreased risk for contralateral breast cancers, as well as an increased risk for bone-related and cardiovascular toxicity. Summary: There continues to be a lack of definitive evidence on the ideal length of adjuvant AI therapy. As certain subgroups may benefit more and experience less toxicity, selecting future patients based on clinicopathologic and genomic factors may maximize the benefit of extended adjuvant aromatase inhibitor therapy while minimizing harms.