Aromatase inhibitors for prevention of breast cancer in postmenopausal women: a narrative review

Objective: The increasing incidence of breast cancer (BC) worldwide has resulted in widespread interest in primary prevention therapies. A number of large randomized trials have shown that selective estrogen receptor modulators can reduce the relative risk for BC by 30% to 40% in high-risk women. In early-stage BC, aromatase inhibitors (AIs) showed a 35% relative reduction in the risk of contralateral BCs compared with tamoxifen. In this narrative review, we discuss the role of AIs in the primary prevention of BC and novel research on combination hormone therapy-medical therapy for the primary prevention of BC. Methods: Using PubMed/Medline, we comprehensively searched for studies of BC primary prevention using AIs, including studies of novel methods of prevention using combination hormone therapy-BC prevention. Results: Two large multicenter, prospective, randomized, placebo-controlled trials have evaluated AIs-anastrozole (International Breast Cancer Intervention Study II) and exemestane (Mammary Prevention 3)-for BC risk reduction in women at increased risk for BC, which we summarize. We identified five studies (three completed and two ongoing) of combination AI-hormone therapy that are undergoing investigation for BC risk reduction. Conclusions: AIs are effective at BC risk reduction, although long-term follow-up data are required to assess whether this risk reduction will result in reduced mortality. Combination hormone therapy-AI for BC risk reduction is experimental and warrants further investigation.