Adjuvant and extended adjuvant use of aromatase inhibitors: reducing the risk of recurrence and distant metastasis

In patients with early-stage breast cancer, all recurrences are associated with an increased risk of mortality, especially distant metastases. Adjuvant tamoxifen therapy for 5 years is effective in postmenopausal patients for the prevention of disease recurrence but is associated with increased risk of rare, potentially fatal adverse events such as endometrial cancer, stroke, and pulmonary embolism. Recently, randomized clinical trials have shown aromatase inhibitor therapy to be superior to tamoxifen therapy for the prevention of disease recurrence. Switching to an aromatase inhibitor after 2-3 years of tamoxifen treatment has been shown to provide superior disease-free survival compared with completing 5 years of tamoxifen. Among approved aromatase inhibitors (letrozole, anastrozole, and exemestane), letrozole is the only one approved as extended adjuvant therapy after completing 5 years of tamoxifen. These results suggest that 10 years of adjuvant endocrine therapy is superior to 5 years of tamoxifen alone.