Extending Aromatase Inhibitor Therapy: Uncertainty Remains

Many studies have addressed the optimal duration of adjuvant endocrine therapy for hormone-receptor–positive breast cancer. Recently, the optimal duration of aromatase inhibitor (AI) therapy for postmenopausal patients has been a focus of deliberation. Several studies have suggested a “sweet spot” of 7 to 8 years' duration. Now, a multicenter, prospective, randomized, open-label Japanese study (AERAS) evaluated the effect of extending anastrozole treatment for an additional 5 years in postmenopausal patients who were disease-free after treatment with either 5 years of anastrozole alone or 2 to 3 years of tamoxifen followed by 2 to 3 years of anastrozole. Between 2007 and 2012, 1697 patients were randomized to continue or stop anastrozole; 9% were previously treated with tamoxifen.

There were fewer cases of local recurrent disease and new primary breast cancers in the continue-anastrozole group than in the stop-anastrozole group (10 vs. 27 and 27 vs. 52, respectively). Disease-free survival (DFS) at 5 years, the primary outcome, was significantly higher in the continue group (91% vs. 86%). Overall survival and distant DFS did not differ significantly between groups. Although rates of bone fracture did not differ, the continue-anastrozole group had significantly higher incidence of arthralgias (37% vs. 29%) and new-onset osteoporosis (47% vs. 44%) and, consequently, higher use of oral bisphosphonates (31% vs. 21%).