Duration of Adjuvant Aromatase-Inhibitor Therapy in Postmenopausal Breast Cancer.

Background: For postmenopausal women with hormone-receptor-positive breast cancer, the most effective duration for adjuvant therapy with an aromatase inhibitor remains unclear.

Methods: In this prospective, phase 3 trial, we randomly assigned postmenopausal women with hormone-receptor-positive breast cancer who had received 5 years of adjuvant endocrine therapy to receive the aromatase inhibitor anastrozole for an additional 2 years (2-year group, receiving a total of 7 years) or an additional 5 years (5-year group, receiving a total of 10 years). The primary end point was disease-free survival. The primary analysis included all the patients who were still participating in the trial and who had no recurrence 2 years after randomization (i.e., when treatment in the 2-year group had ended). Secondary end points were overall survival, contralateral breast cancer, second primary cancer, and clinical bone fracture.

Results: Among the 3484 women who were enrolled in the trial, 3208 remained in the trial without disease progression after the first 2 years of extended anastrozole treatment following randomization. Among these women, disease progression or death occurred in 335 women in each treatment group in the primary-analysis set at 8 years (hazard ratio, 0.99; 95% confidence interval [CI], 0.85 to 1.15; P = 0.90). No between-group differences occurred in most secondary end points, and subgroup analyses did not indicate differences in any particular subgroup. The risk of clinical bone fracture was higher in the 5-year group than in the 2-year group (hazard ratio, 1.35; 95% CI, 1.00 to 1.84).

Conclusions: In postmenopausal women with hormone-receptor-positive breast cancer who had received 5 years of adjuvant endocrine therapy, extending hormone therapy by 5 years provided no benefit over a 2-year extension but was associated with a greater risk of bone fracture. (Funded by AstraZeneca and the Austrian Breast and Colorectal Cancer Study Group; ABCSG-16/SALSA ClinicalTrials.gov number, NCT00295620.).