1. A five-year extension of anastrozole treatment was shown not to provide additional benefit compared to a two-year extension in postmenopausal women with hormone-receptor-positive breast cancer.
2. Anastrozole treatment prolongation was shown to increase the risk of bone fracture.
Evidence Rating Level: 1 (Excellent)
Study Rundown: The most prevalent molecular subtype of breast cancer in women is luminal breast cancer. The risk of reoccurrence continues indefinitely, and more than half of the cases are diagnosed after the first five years. Though treatment extension studies have shown a benefit for longer disease-free survival with tamoxifen, the benefit of extended aromatase-inhibitor therapy is less established. As such, this study investigated the benefits of extending anastrozole, an aromatase-inhibitor, therapy beyond the initial five-year period of treatment in postmenopausal women with hormone-receptor–positive breast cancer. The study determined extending anastrozole therapy for two years was sufficient in maximizing treatment benefits compared to a five-year extension. Furthermore, anastrozole therapy extension was shown to increase the risk of bone fractures. The randomized control trial was limited by using only one aromatase-inhibitor therapy – anastrozole. Additionally, the patients included in the study did not focus on the highest-risk patients with luminal breast cancer. Nonetheless, this study’s results are significant, and its findings highlight the appropriate duration of adjuvant anastrozole in postmenopausal breast cancer.
In-Depth [randomized controlled trial]: This randomized control trial study enrolled 3,484 women across 75 centers in Austria. Participants included in the study were 80 years of age or younger, had histologically verified invasive hormone-receptor-positive breast cancer at an early stage, and received five years of adjuvant endocrine therapy. Participants who did not receive adjuvant therapy up until 12 months prior to randomization were excluded from this study. The participants were randomized in a 1:1 ratio to receive oral anastrozole (1 mg, daily) for either two or five additional years, respectively. The primary endpoint was disease-free survival among patients participating two years after randomization. The primary endpoint was similar between the two groups with disease-free survival at 73.6% for the 2-year group and 73.9% for the 5-year group (hazard ratio [HR], 0.99; 95% confidence interval [CI], 0.85 to 1.15; P = 0.90). Additionally, the hazard ratio for contralateral breast cancer was 1.15 (95% CI, 0.75 to 1.77), and the hazard ratio for a second primary cancer was 1.06 (95% CI, 0.81 to 1.38). The side effects of anastrozole treatment were similar to the known toxicity profile. The most frequently reported adverse event was osteoarthritis with 29 patients in the 2-year group (1.7%) and 74 patients in the 5-year group (4.3%). The risk of a clinical bone fracture was higher in the 5-year group compared to the 2-year group (HR, 1.35; 95% CI, 1.00 to 1.84). Taken together, extending anastrozole treatment for five years after the initial adjuvant endocrine therapy provided no additional benefits compared to a 2-year extension.
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