Background: Breast cancer is the most common cancer diagnosed in Europe, with an estimated 429,900 new cases diagnosed in 2006. For over 20 years, tamoxifen was the standard adjuvant (postoperative) endocrine treatment for hormone receptor-positive (i.e., endocrine-responsive) early breast cancer. Yet, even after the first 5 years, patients with hormone receptor-positive tumours are at risk of relapse. Particularly in endocrine-responsive disease, most instances of relapse and breast cancer mortality occur after the first 5 years.
Scope: Extended adjuvant aromatase inhibitor therapy (EAT) now offers postmenopausal women the opportunity to further protect themselves against late relapse.
Methods: This review summarises the clinical evidence and gives practical recommendations for discussing EAT with patients. Relevant information on patients receiving extended or late extended adjuvant endocrine therapy was obtained from databases and congress websites. The most substantial evidence for EAT is provided by the MA.17 trial using letrozole, with similar results obtained from smaller studies using anastrozole or exemestane.
Findings: Extended adjuvant letrozole reduced the risk of recurrence by 42% and the risk of distant metastases by 40%, it was well tolerated compared to placebo; among lymph node-positive patients, overall survival was significantly improved. Ideally, EAT should be started within 3 months of finishing tamoxifen therapy, and evidence supports its use for at least 4 years, showing increasing benefit with longer treatment duration. It is also effective, even after a longer time period, following completion of tamoxifen therapy. When deciding whether or not to use EAT after tamoxifen, clinicians and patients should consider the residual risk of relapse, comorbidities and individual preferences.