Extending hormone therapy by five years does not provide benefit over a two-year extension among postmenopausal women with hormone receptor-positive breast cancer who had received five years of adjuvant endocrine therapy, according to a study published in the July 29 issue of the New England Journal of Medicine.
Michael Gnant, M.D., from the Medical University of Vienna in Austria, and colleagues conducted a phase 3 trial involving postmenopausal women with hormone receptor-positive breast cancer who had received five years of adjuvant endocrine therapy. Participants were randomly assigned to receive the aromatase inhibitor anastrozole for an additional two years or an additional five years. Disease-free survival was the primary end point.
After the first two years of extended anastrozole treatment following randomization, 3,208 of 3,484 women remained in the trial without disease progression. The researchers found that in the primary analysis at eight years, disease progression or death occurred in 335 women in each treatment group (hazard ratio, 0.99; 95 percent confidence interval, 0.85 to 1.15; P = 0.90). For most secondary end points, there were no between-group differences; no differences were observed for any particular subgroup in subgroup analyses. Compared with the two-year group, the five-year group had a higher risk for clinical bone fracture (hazard ratio, 1.35; 95 percent confidence interval, 1.00 to 1.84).
“At a median follow-up of nearly 10 years (i.e., a median of 15 years after the first diagnosis of breast cancer), we found that a five-year extension of adjuvant therapy with the aromatase-inhibitor anastrozole was not associated with a better outcome than a two-year extension with respect to disease-free survival,” the authors write.
The study was funded by AstraZeneca, a manufacturer of anastrozole.