The ATENA phase III randomized parallel-group multicenter trial is designed to compare 5
years of adjuvant exemestane versus 5 years of observation in postmenopausal women with
operable breast cancer who have received 5-7 years of adjuvant tamoxifen. The primary
endpoint for the core protocol is disease-free survival (DFS). Exemestane treatment is
planned for 5 years unless disease relapse or excessive toxicity is documented, the patient
refuses further treatment or any new anti-cancer therapy is initiated.