The primary endpoints were the disease-free survival, and the secondary endpoints: time to recurrence, time to distant recurrence, incidence of new contralateral breast cancer, overall survival, and death with or without recurrence in all randomised patients (anastrozole n=3125, tamoxifen n=3116) and hormone-receptor-positive patients (anastrozole n=2618, tamoxifen n=2598). After treatment completion, they continued to collect data on fractures and serious adverse events in a masked fashion (safety population: anastrozole n=3092, tamoxifen n=3094).

There were 24 522 woman-years of follow-up in the anastrozole group and 23 950 woman-years in the tamoxifen group. In the full study population, there were significant improvements in the anastrozole group compared with the tamoxifen group for disease-free survival (HR] 0•91, 95% CI 0•83-0•99; p=0•04), time to recurrence (0•84, 0•75-0•93; p=0•001), and time to distant recurrence (0•87, 0•77-0•99; p=0•03). For hormone-receptor-positive patients, the results were also significantly in favour of the anastrozole group for disease-free survival (HR 0•86, 95% CI 0•78-0•95; p=0•003), time to recurrence (0•79, 0•70-0•89; p=0•0002), and time to distant recurrence (0•85, 0•73-0•98; p=0•02). In hormone-receptor-positive patients, absolute differences in time to recurrence between anastrozole and tamoxifen increased over time (2•7% at 5 years and 4•3% at 10 years) and recurrence rates remained significantly lower on anastrozole than tamoxifen after treatment completion (HR 0•81, 95% CI 0•67-0•98; p=0•03), although the carryover benefit was smaller after 8 years. There was weak evidence of fewer deaths after recurrence with anastrozole compared with tamoxifen treatment in the hormone-receptor-positive subgroup (HR 0•87, 95% CI 0•74-1•02; p=0•09), but there was little difference in overall mortality (0•95, 95% CI 0•84-1•06; p=0•4).
Fractures were more frequent during active treatment in patients receiving anastrozole than those receiving tamoxifen (451 vs 351; OR 1•33, 95% CI 1•15-1•55; p<0•0001), but were similar in the post-treatment follow-up period (110 vs 112; OR 0•98, 95% CI 0•74-1•30; p=0•9). Treatment-related serious adverse events were less common in the anastrozole group than the tamoxifen group (223 anastrozole vs 369 tamoxifen; OR 0•57, 95% CI 0•48-0•69; p<0•0001), but were similar after treatment completion (66 vs 78; OR 0•84, 95% CI 0•60-1•19; p=0•3). No differences in non-breast cancer causes of death were apparent and the incidence of other cancers was similar between groups (425 vs 431) and continue to be higher with anastrozole for colorectal (66 vs 44) and lung cancer (51 vs 34), and lower for endometrial cancer (six vs 24), melanoma (eight vs 19), and ovarian cancer (17 vs 28). No new safety concerns were reported.
Interpretation
These data confirm the long-term superior efficacy and safety of anastrozole over tamoxifen as initial adjuvant therapy for postmenopausal women with hormone-sensitive early breast cancer.