After undergoing 5 years of adjuvant endocrine therapy, 2 years of extended anastrozole proved as effective as 5 years for preventing breast cancer recurrence among postmenopausal women with hormone receptor (HR)-positive breast cancer, according to the results of the ABCSG-16 phase III trial presented at the 2017 San Antonio Breast Cancer Symposium (SABCS), held December 5–9.
The study included 3,484 patients with HR-positive disease who were followed for a median of about 9 years. There was no difference in disease-free survival among women who received 5 years anastrozole (70.3%) and those who received only 2 years (71.1%; hazard ratio [HR], 1.007; 95% CI, 0.87–1.16). There was also no difference in overall survival between the two groups (84.9% vs 85.3%).
According to Michael Gnant, MD, FACS, director and chairman of the department of surgery, Comprehensive Cancer Center, at the Medical University of Vienna, who presented the results, the only significant difference between the two groups was in the number of fractures. The incidence of fracture was 6.3% in patients assigned to 5 years’ treatment compared with 4.7% in the 2-year group (HR, 1.353; 95% CI, 1.00–1.84; P = .053).
Women with HR-positive breast cancer have a significant long-term risk for relapse. In fact, it has recently been shown that more than 50% of all relapses occur after the first 5 years of follow-up in this breast cancer type. According to Gnant, because of this risk, physicians have a tendency to extend the duration of adjuvant hormone therapy, but questions remain about the optimal duration of extended adjuvant aromatase inhibitor therapy?
Based on the results of this study, Gnant said “there is no benefit of continuing/escalating endocrine treatment beyond 7 years,” but he cautioned that researchers cannot rule out benefit for some patients who take anastrozole for longer periods.
Gnant said future translational research using data and biomaterial from the patients in the ABCSG-16 trial could be useful to characterize potential molecular factors that influence patients’ response to anastrozole.