Endocrine therapy plus zoledronic acid in premenopausal breast cancer.

After a median follow-up of 47.8 months, 137 events had occurred, with disease-free survival rates of 92.8% in the tamoxifen group, 92.0% in the anastrozole group, 90.8% in the group that received endocrine therapy alone, and 94.0% in the group that received endocrine therapy with zoledronic acid. There was no significant dif ference in disease-free survival between the anastrozole and tamoxifen groups (haz ard ratio for disease progression in the anastrozole group, 1.10; 95% confidence in terval [CI], 0.78 to 1.53; P = 0.59). The addition of zoledronic acid to endocrine therapy, as compared with endocrine therapy without zoledronic acid, resulted in an absolute reduction of 3.2 percentage points and a relative reduction of 36% in the risk of dis ease progression (hazard ratio, 0.64; 95% CI, 0.46 to 0.91; P = 0.01); the addition of zoledronic acid did not significantly reduce the risk of death (hazard ratio, 0.60; 95% CI, 0.32 to 1.11; P = 0.11). Adverse events were consistent with known drug-safety profiles. Conclusions The addition of zoledronic acid to adjuvant endocrine therapy improves disease-free survival in premenopausal patients with estrogen-responsive early breast cancer. (ClinicalTrials.gov number, NCT00295646.)